When we can have both btc and BU co exist, why not treat BU like another Altcoin similar to btc?.
Why can't both compliment each other?
It is easy to say but it is hard to do. Creating codes such as segwit codes, bitcoin unlimited and other codes is a very complex job and how much more integrating them. The much easier choice is to create a consensus that all miners will use one universal code so that bitcoin will solve its problems. But even reaching a consensus is hard then how much more it is to synthesize all codes into one.