Because they look beautiful?
I’m sitting next to one of these Chinese camphor chests right now and certainly not going to get rid of it because it needs special care. https://chairish-prod.freetls.fastly.net/image/product/master/6ced114c-af7b-4599-88ee-fc0bfb44f360/early-1900s-chinese-oriental-hand-carved-camphor-chest-9391
It’s been in our living room for 25 years and coasters have kept it unmarred (we have a nice set of cork-backed coasters with Van Gogh designs, a gift my sister found at a museum store)
We have sandstone coasters like these. They are beautiful and very absorbent.
I have $10 Target tables, and I use coasters(metal Wally world ones, but I do have a large collection of paper coasters from various bars.)
Ooh! Just thought of a craft project for the grand-wreks to make out of my 550 wooden coffee stirrers. Yay!
I own a total of zero coasters. That is plenty for my needs.
I live alone and entertain very rarely, so my coaster needs are few.
My everyday, always by-my-easy-chair one, is made of ground-up tires, reconstituted into a round shape. Just plain black; nothing fancy.
Back in the day, when I could have friends over to watch sports on TV, they’d get either pub mats advertising various beers, or (just to change things up), coasters with the logos of NHL teams on them. I well remember the time when I handed one of my friends a coaster bearing the logo of the Toronto Maple Leafs. He hates the Leafs, and didn’t want that, but since I had none bearing the logo of his Ottawa Senators, was happy to settle for a coaster bearing the logo of the Detroit Red Wings.
The irony? We were gathered at my place to watch an NFL football game.
Got sandstone coasters as well, but in green. Also cork coasters. The ones we use the most are felt coasters (from daff) and we also use felt placemats. They don’t stick to the mug and they are handwashable.
And so much quieter than sandstone.
I would love to, but the amusement parks aren’t open right now. 
We have those stone coasters but they are all put up since the 1 year old like to use them to beat on the furniture. I’ve got some pine ones that a distillery who’s board I’m on gave out as presents at the board meeting this year that I still haven’t unwrapped.
Between the dogs and the children we’ve decided our furnature (from our 20s) is basically garbage and we’ll replace it in a decade once they’ll quit destroying it.
We have a bunch of wooden ones, with cork insets, which I think came from Crate & Barrel about 25 years ago.
Being the gamer nerd that I am, I also have some felt coasters which are shaped like polyhedral dice; those only get used when we’re hosting games.
I do own nice wood coasters somewhere, but normally if I have the need I’ll just grab two tissues and fold them into a square.
However the need is quite rare as I either drink right from the can/bottle and use a koozie (I have cool wood ones I bought in Montana) or I drink from Tervis tumblers or knockoff YETI-style insulated cups that don’t condensate or transfer heat.
Yep. Cheap furniture, and the only things I drink are coffee in an insulated mug and water in a different insulated mug. I’m honestly surprised to hear that coasters are such a big thing.
If I got coasters, they would be the newest, nicest, cleanest things in my living room. I certainly wouldn’t want anybody setting any drinks on them.
We have a sandstone set exactly like the ones Panache45’s link shows. We also have a dozen or so leather coasters with our bank’s logo. Our daughter worked at our bank until about a week ago and brought them home. Maybe her new bank will have some coasters too
Wow, the first step to adulthood for me was getting coasters from the bars I worked at for the apartment.
Tallahassee is hot and humid and drinks sweat like mad.
I have a set of cork coasters with my grandfather’s initials. People often ask me why my coasters have those initials. 
I also have some nice Japanese yosegi coasters, a souvenir from a trip to Japan. And some cool wooden coasters shaped like Escher lizards.
I think the only coasters we ever bought are from Ikea, nicely sculpted pucks of silicone in cool colours. We also have a set of slate coasters (engraved with Chrysler car brands :o) that my hubby was given at work, a stack of silver-plated coasters I inherited when my weird uncle passed away, and some coated cardboard ones with Van Gogh images on them from my (late) in-laws.
For a while there I had a set of coasters that were the pieces of wood cut out of the tops of acoustic guitars to make the soundhole.
They were sort of cool. but didn’t last as the wood tended to split along the grain when they got wet