Before FTX collapsed in November 2022, it was the third-largest exchange in terms of volume and had over one million users. The market size and age of a company don't guarantee that it is reasonable. People trusting some altcoins doesn't make them reliable, it could be because of ignorance. The discussion is about conducting a comprehensive audit of Tether. Until it is done, USDT remains a risky currency to keep.
If not age what else is there? Name a few indicators.

Surely some remember Wirecard, audited and still went belly up.