The concern is that most methods of trading fiat to Bitcoin on P2P DEXes are KYCed and could easily be forced to restrict transactions in that manner. Aside from cash by mail (which is immensely risky), it'd be difficult to implement a truly uncensorable means of buying Bitcoin through a DEX.
Discussion
Connecting with peers at meetups and building a social network for peer to peer transactions is best.
But bank transfers that are independent of your Bitcoin purchases are still vastly better than KYC'ing yourself on an exchange.