I would trust a reputable bank more than a stablecoin, stablecoins are just centralized payment systems that exist in a form of cryptocurrency. This means that just like banks, they can have a bank run, or they could make an exit scam and so on. Besides, if you're selling Bitcoin for fiat, you probably want to use that fiat for something, like buying a car or a house, and it's hard to do that with stablecoin.
why I should exchange my coins for some stable coins?
ok if there are some conditions on the market but generally it's just a mistake since I am assuming the risk of having funds in something that could be sized or blocked from a central authority, definitely an option that I want avoid.
Plus crypto market is rising nowadays, I don't think it's a good choice invest on stable coins.
Temporarily, to lock in, until you cash out