I don’t see how cryptocurrency trading could be considered legal while at the same time avoiding regulation by governments? If you were to imagine a scenario in which there is no CEX, only DEX - how many people do you think would trade Bitcoin today, and how many people would know it even exists?
Lest anyone misunderstand, I understand that decentralization is very important, and that it is bad that CEX holds such large amounts of BTC in its possession - but since most people have never accepted (or realized) how important it is to be their own bank, consciously we agreed to go in a direction we might not have needed to go.
As for the number of crypto exchanges, I think there are more than there should be, and it should be regulated who can start such a business. Too many people have seen an opportunity to get rich that way, and in many cases this results in hacking and losing clients ’funds, or with an exit scam.