Even if it was 1 to 1 backed by the corporations that claims they are backed by real fiat (which some even came clear about not being 1 to 1 backed anymore so I don't know why they are worth like that) its still not the same with bitcoin. There is always risk of printing more, there is always risk of centralized issues of withdrawing money from the market, and the biggest threat of all there is always an issue of "lol gotcha" of the corporation that reeped the benefits of it and than leave as an exit scam.

Why would anyone prefer stablecoins over bitcoin I don't know, if you want to use regular fiat just use fiat anyway, there is no one stopping you to use dollars for example, that is what many people do, if you want to use bitcoin than use bitcoin but if you use tether for example that is neither as safe as bitcoin nor as accepted as dollars so whats the point.