It all comes down to a lack of understanding. I think the convenience versus security aspect plays an important role here. People aiming for convenience will choose to go with centralized exchanges that are subject to all sorts of thefts. People aiming for security, and thus make use of decentralized exchanges, will enjoy less convenience. If we realistically look at how these exchanges will/might evolve, I am not really expecting a lot to change in the coming years -- lack of fiat trading in a decentralized way is a killer.