Well, to answer a lot of those questions, here's some info.
This game was a collaboration between myself and an artist, with me doing the weapon/gameplay effects, sound, music, and misc edits on sprites. Also had to do things like menu stuff and the title. The artist did the rest, including the backgrounds. enemies, asteroids, H sprites, the gallery image etc. I tried to avoid doing massive edits as much as possible, since the game's profits were split 50/50, and if I edited all his work it would have defeated the purpose a bit.
Basically, the original plan for this game was that I would make literally just a copy of asteroids; no levels, no weapons, the only difference being that the enemy ships would be different aliens as you go, and would be able to H the player. The goal being to give the artist something he could edit by himself in GM and release updates to without any input from me. That's why it was asteroids. Problem was, gradual ideas like "what if there were enemies in the asteroids?" and "may as well add a couple weapons" took over. By the time I added a couple things, it was already more than what he could program.
After 3-4 weeks of him doing graphics, he had to get back to doing commissions (which he does for a living), so I basically had to do what I could with what I had, without adding too much, and without spending so much time on the game that it would be pointless, since I don't expect to make a lot of profit from an asteroids style game.
In other words, the answer to most of those questions is because it was what I could do with what I had, or because I had to settle so that it didn't take any longer than it did. Needless to say, if I knew that it was going to be something I'd have to do full sound design and music for, I certainly wouldn't have chosen asteroids.