Many users still have doubts about what kind of stablecoins are generally backed by real dollars. But if there was a real threat to the security of storage, it is unlikely that stable coins in particular USDT would be so popular.
USDT is so popular because it first introduced the concept of stablecoins and hence it has a unique identity and liquidity in the market. It's similar to why despite better coins available there are some other old coins still popular in the market, that is because they arrived first and have a user base which use them and are habitual to it.
I usually trade at Binance and I prefer BUSD over USDT now days, but a trader who doesn't use Binance would always prefer tether USDT because it has better liquidity and trading volume.
I myself quite often use Tether to safely store my assets because its rate is more or less stable and it is backed by the usual US dollar. Although now many are already switching to BUSD, due to the active development of Binance. In general, I think that stable coins are the most reliable currency in terms of rate volatility.
Being reliable is confusing because I rather prefer Bitcoins in terms of reliability as opposed to tether or any stablecoins but in terms of stability, I prefer tether above Bitcoin.