Well, The Knot is hardly an important tool. Most people I know don’t use it – it certainly wasn’t used in our family – no matter the size of the wedding. It’s a place for people to get ideas and usually tends to draw the budget-conscious bride and groom.
In the larger weddings, that’s exactly what it is. It’s not really as much a party for the bride and groom as a party for the family and friends. It was an excuse to get all the people together than you haven’t seen in donkey’s ages and drink, eat, and dance too much together. I understand this is not for everyone but a lot of people do have big family and big circles of friends and like to have an excuse to throw a big party. Weddings are fun. Or at least I think they are.
“Really big” is going to depend on a lot of things - to some extent SES, ethnicity and also location. There’s also the question of defining “aren’t even people they know well” - I mean my wedding* 34 years ago included my mother’s 40 first cousins and their spouses. I know them - but how well is a matter of opinion. I certainly didn’t see them much by the time I got married , but I saw them frequently when I was a kid.
What I don’t understand is something I sometimes hear about when people are talking about plus-ones. There['s always someone who says they literally don’t know anyone except the bride and /or groom, so they won’t have anyone to talk to if they can’t bring a plus-one. What I can never figure out is who is getting invited to a wedding where they don’t know anyone except the couple- a relative should know other relatives, a coworker would know other coworkers and one would think that a friend would know other friends and possibly even some relatives.
* The one that was mainly my family and had 200 guests. There was another reception a few weeks later that was mainly my husband’s family and had about another 200 guests. Only 30-40 people attended both - I’m of half-Italian descent and he’s of Chinese descent.
I have a friend from graduate school. We shared a little office together and became good friends. He and his now wife were from another state and that’s where the wedding was. We had some friends in common but I was the only one who chose to fly out to the wedding. I could have brought my girlfriend at the time but she didn’t end up going for reasons that I don’t recall. The wedding guests were family of both sides and hometown friends.
I think I had met his brother one or two other times and also one or two of the friends once briefly when they came out to visit and he showed them the lab. I effectively didn’t know anyone there except the bride and groom.
I’m about to go to the wedding of someone I barely know. My second cousin is getting married in July, and while I’ve certainly met him, he’s ~15 years younger than I am and I don’t know him well.
But I got invited and a whole bunch of extended family will be there that I’d like to see. I don’t know how large the wedding is, but by virtue of the fact that second cousins like me are getting invites, I assume it’s pretty big. My wedding was 150 people and the current groom’s dad (my first cousin) didn’t make the cut for an invite.
I was the +1 for a wedding with a girl I was seeing very casually. She was the only one I knew (barely, I can’t remember if I ever knew her last name) at the reception and it was awkward meeting her parents who she fought with the whole night.
Another time, I went to the reception of a college buddy and he was the only one I knew. At least he was the groom. They sat me at the table with the other vendors (dj, photogs, video, planner, etc), lol. It was fine, they were probably easier to chat with than some kids or elderly relatives or something.
It was really disappointing to receive notice from a cousin a couple states away they they had canceled their reception later this summer (after canceling it last summer). There are about 15 aunts and uncles and dozens of cousins on that side of the family and, without weddings, I’d basically never see a lot of them. I suppose there will be funerals 
At the wedding I described above:
I didn’t know anyone other than my husband and the bride and groom, whom we had met in college. It was a small weekday wedding. We happened to live in the town where it was held so we only had to take off an afternoon to attend. None of their other college friends (who weren’t local) came. I guess she had a few friends from her hometown, and he had… a handful of relatives and us.
That was a pretty weird wedding, though.
That’s why I asked in In My Humble Opinion. I wanted more of a feel, if the TV show situation rings vaguely true or vaguely false to some Americans who felt like answering.
I would just like to point out that the OP refers to typical American weddings, and not ethnic weddings. I would add that I also get the impression from Hollywood that American weddings are big and expensive, but this obviously cannot be so, as a second or subsequent wedding will be much less lavish and most likely with fewer guests.
Having been an expatriate for so long, I missed the wave of weddings of friends a few years out of university. The ones I went to the the UK were not big, at most maybe a hundred people, and all involved relatives. Polish weddings are bigger, but probably no more than about 150 people. But, a two day reception. Day two tends to be the walking dead, and some decide to give it a miss.
My own wedding in Poland was a very small affair, for various reasons, with maybe 30 people, all of whom I knew.
The Middle East and Asia have a tradition of huge and lavish weddings, but I have never been to one, apart from a wedding in Japan that was rather more Western-style and not that large. I knew nobody there, as my GF of the time knew one of the bridal pair.
It would depend on what you mean by “barely know.” I’ve been to weddings of people from my church who were not in my immediate circle of friends, but I’ve always been at least on a first name basis with at least the bride or groom, or at least their parents. (Well, sometimes my parents knew them and I was dragged along.)
I’m not quite sure what I would consider a typical wedding size. I guess a few dozen people, maybe? It’s been a little while since I’ve been to one. I do note the reception (the part where we eat) is usually larger than the wedding proper (the part with the ceremony, where they are “pronounced husband and wife”).
(And, no, I’ve unfortunately never been to a same sex wedding. Everyone I’ve known has eloped.)
I’ve been to two. The food is on average better and the decorations were fabulous. 
Seriously, those were two of the most touching ceremonies I’ve ever attended. Watching folks whose basic human rights were only now being legally recognized years after their relationship had gone permanent. Helping them join the ranks of the “officially coupled” for lack of a less clumsy term. Both in the law and in their religious tradition. That meant a lot to everyone in attendance regardless of their orientation.
“I’ve never been to a wedding where I didn’t know one of the couple quite well - but I have been to some weddings where some of the guests were friends of the parents of the couple more than being friends of the couple.”
Including our wedding. A number of my father’s friends from his office came to our wedding, including his boss. (He and my mother had attended his friends’ kids weddings over the years.)
It really depends on the type of wedding as well. Growing up, most of the weddings I attended were at the Baptist church. After the ceremony, there was punch, coffee, cake, and cookies in the fellowship hall. No dinner, no bar, no dancing, no band. Pretty inexpensive and it wasn’t unusual for the bride to invite the whole church congregation. Keep in mind the whole town had fewer than 1300 residents.
I think I’ve been to six weddings in the past 30 years. From 30 people to 400.