Stablecoins actually gained popularity. Why? Simply because having stablecoins eliminates the risks of volatility through assets like bitcoin. Along with that, not everyone(or probably even majority) don't even care about decentralization and security in the first place! This is the exact reason why for some reason people still "invest" in other cryptocurrencies like XRP, and other worse shitcoins.
Also, the popularity of these seems more likely a result of low bank interest rates as well as the negative interest rates that the banks have enforced in developed countries. Anybody would be better off earning interest from staked collateral as an alternative investment. This is not so applicable to the retail investors in developing countries because the interest rates at similar instruments hasn't reached similar abysmal levels yet.