This is exactly why stablecoins like USDT, TUSD, DAI, Libra, etc. won't gain much popularity. Cryptocurrencies and the blockchain technology were created with a scope - that we get rid of all the centralization and excessive control of authorities over the world. Corruption is at all time high level and transparency is nowhere near where we would like it to be. By adopting Bitcoin and blockchain & adiacent tech like smart contracts I'm sure we will make a much efficient & fair world.
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.
I am not sure if Tether and TUSD with their unsubstantiated claims of "fiat backing" can be considered stablecoin. Though something like MAKR DAI does seem like a stablecoin because of the locked cryptocurrency that backs them.
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.