The problem crypto has is simple: You can't pay your rent in crypto, and you can't earn crypto as salary. So you need an intermediate to convert it to/from fiat. And you need to keep using fiat. Therefore you need a way to convert.
The most decentralised is something like localbitcoins, but for most people its too much hassle. It's like selling a second hand car type process (which most people hate) just to get cash to spend. Therefore a centralised bank it much more preferable.