Beginning something with ‘So’ seems faddish to me. Albeit an irritating fad that simply displays the users poor knowledge of grammar, but a fad none the less. As such it appears more popular among younger people who are more susceptible to ‘monkey see, monkey do’ type mannerisms. They hear it on TV or pick it up in their social circle and so it goes. Before you know it everything that comes out of their mouth is prefixed with ‘So’ and they likely don’t even realize that they sound like an under educated buffoon.
Similarly, if you listen to television commercials you’ll notice the writers have the actors emphasize a particular phrase or mannerism. To most this is annoying, but they know kids will pick it up and mimic it.
Language usage has been declining for a number of years and I don’t expect things to change anytime soon. As a matter of fact I suspect we’re stuck with it.
What’s worse to me is initialisms. It seems there’s not a corporation on the planet that goes by their proper name anymore. WW. Really? It’s a lot easier to say Weight Watchers, but that wouldn’t be on trend. It also wouldn’t sound so stupid.
Any written, and even spoken account of anything is rife with initialisms. No one knows what the hell anyone is talking about. Sometimes it can be sorted out through context, but generally speaking you can find something like PYZ and RPM scattered throughout. Huh?!
Some common ones have become well known and generally understood but often I’ll see an advert for some company named QGI with no hint of what it’s supposed to stand for. As though in their mind they’re so well known that people will just know. Newspaper stories are big on the offenders list. I’ve even heard news readers use intitialisms. How much longer does it take to say 3 words than 3 initials? Dumb.
Why are we starting with “so” and ending with “right?”
So… this is something that annoys everyone, right?
Exhibit number 50,803 of why the SDMB doesn’t attract younger posters.
For a long time, the go-to meaningless phrase was “you know”. That pretty much reached a peak with Caroline Kennedy.
And the Black phrase, “you know what I’m sayin’?”.
Next thing you know they’ll start replacing a perfectly good three syllable word with VW! Kids today…
So, as Chaucer is, shall Dryden be?
Just another example of people using linguistic markers to exclude others from their own group. It’s what drives the evolution of language.
This is how I see it being used and how I often use it. Say a group of people involved in small talk. One mentions the weather. Another agrees it’s been getting colder. Another looks forward to winter. Pause in conversation. No one else has anything to add to the topic. Someone else begins… “So… How about them Cubs?”
For whatever reason, the pandemic has heightened my awareness of “… and so …” as a mild irritant.
And – just like when you buy a new X color car of Y make and Z model – you begin to notice them everywhere – I’m hearing “… and so …” constantly.
It’s enough to drive a person to drink (he said, hoping to imply – comically – that this was something even remotely akin to a strong statement).
I first noticed it a dozen or so years ago on the Canadian science show Quirks and Quarks, CBC radio 1 at noon every Saturday. The interviewer asks a question. The interviewee starts out, “So,…”. Whoever suggested above that it is a placeholder while collecting thoughts. It has just replaced, “Umm,…” and is totally harmless. Get over it.
It’s the first word of Seamus Heaney’s translation of Beowulf.
Yeah, I definitely feel “so” often carries this purpose, as well as signifying that what is about to follow is not a simple thought but a larger narrative. For example, if you answered the question “where did you go last night” with “so, I went to the store” instead of “I went to the store,” that sounds abrupt and cuf-off to me, not the way an English speaker would use an introductory “so.” I would expect more information to follow, and that information was signaled by the “so.” “Well,” also serves the same or similar function in this type of case.
As far as using it, I know I personally have to constantly scan my written prose for overuse of the word “so.” It’s pretty natural to me. I’m 46 and I don’t ever remember “so” not being a part of the speech of me and my peers.
For a reasonably scholarly discussion from a real linguist, listen to
Nu? Because you goyim can’t get away with saying “Nu”. 
There’s a purpose for something like that in spoken conversation - the first part of anything is the most likely part to be missed, misheard, or drowned out by background noise etc - padding the start of a spoken sentence with something that indicates ‘I am speaking now’ allows the listener a moment to tune in and pay attention without missing anything.
It’s not limited to English - I don’t know about other languages, but starting a sentence with “so” (“az”) is very common in Hebrew as well. Just a WAG: it came from Yiddish, originally, which may also be how it became so common in American English.
I figure it’s just a way of announcing that you are going to be speaking soon, so you get the listeners attention.
I listen to The Moth, a radio show/podcast where people tell real stories about their lives. I think in about half of them the the first word is “so.”
In my youth, the placeholder of choice at the beginning of sentences for most interviewees was “Well…”
At some point in recent years, it switched to “So…”
Either placeholder, it seems to me, serves the same function. It buys the interviewee some time to organize their thoughts.
And yes, the switch from “well” to “so” bothered me, mainly because “That’s not the way we used to do it!”
Also sort of an in medias res indication.