Is there some reason why the mining software like
bgminer are not on homebrew? I guess I'm wondering if there is a "political" reason? or if it's just not been tried yet? or is there some other reason?
Profitable mining is done by fairly few individuals today (unfortunately), and so there is not really much demand for an easily installable mining client. Most professional mining operations likely compile their own mining clients from source, possibly with their own customizations.
The only demand I could see, which I suspect is your usecase, is to just try mining out for fun. That reason alone hasn't been sufficient enough for someone to spend the time to get a mining client on brew/macports/etc.