I think it is to deal with data caps. And brute force is always possible if one has the 4-way handshake and the password is only useful if you are near enough t

I think it is to deal with data caps. And brute force is always possible if one has the 4-way handshake and the password is only useful if you are near enough to actually connect to the network. AFAIK the PSK uses PBKDF2.