The author is a shoujo mangaka drawing a shounen manga only this time, but I guess she couldn't help herself with having many guys and few girls, just like in a shoujo manga. A new girl is most welcome.
I guess that's his problem on purpose. The old club, before the seniors graduated, only had him as a follower, but after being left alone, he's the senior and thus naturally also the president. He's not really suited for it, it just happened with nobody else around. However, so far the club only has a bunch of ex-delinquents and one genius who can't cooperate, so ironically he's still the best man for the job.