Yeah, it's hard to imagine one party going on all these adventures. Then again, with how lethal Ravenloft enemies tended to be, I suppose there's a lot of attrition to consider.
I kept trying to run and play Ravenloft, but the general consensus among the old salts I know is that when someone mentions running a Ravenloft game, there's a collective groan.
We had met to discuss who would run a campaign a few years back, and this one new DM was all excited when he proposed a Ravenloft game. Cue the groans and him being very confused. "Ravenloft is great, I love Ravenloft, what's wrong with it?"
So we told him. Railroaded into a setting designed to be miserable, with enemies who are supposed to instill you with gothic terror, but are basically overtuned to the point you feel less like heroic adventurers, and more like a bunch of dumb kids who decided to camp out at Lake Crystal or some old cabin in the woods. I told him I'd give it a chance, but my roommate still had PTSD from a 4e adventure where poltergeists possessed household items and he almost died to a polterofen (that's a ghost possessing an oven by the by).
Heck, the AL Curse of Strahd tie-in adventure was so brutal that the only reason I survived was I had a legacy Yuan-Ti Paladin (the magic resistance was useless as the DM ruled against it working on anything that wasn't a spell, lol, but the immunity to poisoned was huge, and well, a Paladin is the hardest thing to kill in 5e as near as I can tell), and we still got a character perma-killed by disintegration in the final battle and another permanently trapped in Ravenloft, lol.
Though to be fair, Tomb of Annihilation was much, much worse. People were quitting rather than risk losing their characters, lol.