Unattractive male leads in porn aimed at men are common and have a purpose: They improve the fantasy when the reader/viewer places himself in the position of the character. The line of thinking that it generates boils down to "if this ugly schlub gets this much tail in this situation, imagine how much _I_ would get." You see something similar with power fantasy porn and the stupid mistakes the protagonists make.
There is also some carryover from the RL adult film industry, where the pool of male leads is restricted by the need of them to be able to get it up, and keep it up, on command.