If you mean banks, that is a specific need because only they can digitize cash. In this case, @op specifies the definition of the term "middleman" as not being the bank itself (unless they also provide recommended bitcoin traders directly).

And like I said before that "trust" is the concern. When it comes to making transactions on the internet, at least it is easier for users to trust centralized exchanges because they are regulated, or p2p exchanges where they have a list of verified traders and are considered capable of resolving disputes.