Bah, its like you guys haven't even put hours into contemplating erotic game design. What's wrong with you? Are you some sort of degenerates?
There are two reasons for why the protag is the way he is. One was stated by the developers, the other I can infer based on my uh friend's thorough experience with the genre.
According to the devs, introducing facial features exponentially increases the amount of work required to produce an animation. If the choice is between being able to see your dude's face and having more animated sex scenes in the game, I suspect that the majority of people will go for the latter every time.
Based on the pre-release voice reels and character bios we can see that the protagonist does indeed have a personality and a backstory that connects him to other characters (he also has a very particular accent and we all know what that means.) He also seems to be a pretty generic and humorous character. In my...informed opinion, this type of character suits the game for the same reason why the male part of black-tie dress code is, well, black - it allows the ladies to stand out. But moreover, the more developed the protagonist of an eroge game is, the narrower its target demographic will be. If the protagonist was an assertive douchebag ala Rance, then that would scare off people looking for femdom. If the character was a submissive pushover, that would frustrate people looking for maledom, and so on (not that you can't subvert this dynamic by having a dominant person in a submissive position or a submissive person in a dominant position ((see: Sanguine Rose)) but again this would make for a rather particular story that won't appeal to as many people.) So if Studio FOW is trying to hit as many people as possible with their first game, they probably want to go for a relatively generic protagonist.
I do understand the concerns that gay and bisexual Codexers such as
jf8350143 have brought to this discussion and for them I suggest only that they
investigate this thread for they may find it to be of great interest.