Easily destroyed by fire-fighting planes dropping Dawn dishwashing liquid.
I don’t discount most of your premise but I think this bit here might not be right. Mammoth is rare, maybe, among discovered caves, but who knows how many other larger caves are out there yet undiscovered?
During the Ice Ages, there were cave lions, cave bears, and even cave hyaenas. I suppose they did most, or all, of their hunting outside the cave, but you wouldn’t want to meet one if you were down there to do a bit of petrography.
Sarlaccs can live for tens of thousands of years but hutts for perhaps 1000. Jabba was 606 years, old [(Hutt | Wookieepedia | Fandom). A sarlacc seems like it would be difficult to relocate, once established.
If you’d have told me last night I’d spend quite a long time reading about hutts today, I’d have laughed in your face.
Tremors is from 1990, the V episode from 1984. The Tremors creature looks like a crivit. (And the person being killed looks Time Lord.)
OK, so maybe the sarlacc was put there by Jabba’s ancestors, or maybe it’s still a relatively young specimen. However it got there originally, it’s certainly surviving now by being actively fed by Jabba.
Lots of things can survive in environments they’re not evolutionarily suited for, with the intervention of sapient, technological creatures.