BTC wasn’t stable because people used and speculated on it. Very few people speculate on Monero since “it could be banned any day now” (9 years in lol) and a decent amount of people actually use it.

I would assume less of Moneros OG coins were lost than with bitcoin where the entire concept of crypto was still new so there are probably a few more whales as well as more coins in circulation. That probably also has an effect on our volatility.