because that is the simplest voting system and i had enough "trauma" from writing a voting website app years ago that i somehow didn't consider supporting multiple voting systems. in retrospect this was not a very good idea and it probably needs a bit of work.
honestly the apioforum voting system has always been slightly half baked. there's still no way to close polls, or any way to see who is voting for which options in one place.
contributions are always welcome of course. if you want to learn git i would recommend the official git book, which you can read for free on their website.