If you're sitting on millions worth of crypto, you either got extremely lucky, or you're extremely wealthy. If you're sitting on $100k worth, you can easily spend it for everyday uses without exposing yourself. There are groups where you can exchange FIAT => Crypto and vice versa, where you meet up face to face and do the deal. Similar to LocalBitcoins.
Demand for DEX's will explode eventually, no doubt.
Many people try to avoid just this (I marked in bold). This carries great risks and contradicts anonymity.
As for the demand for DEX, it already exists, but there is no fiat. If it was there, then I think this "explosion" would have already taken place.