That's the big difference between international rules and blackball rules in English pool and it's never sat right with me. I prefer blackball rules where pocketing your ball and the opponents ball in the same shot is legal (presuming you hit your ball first), but if you try it and fail it's a foul.
Ultimate pool was originally a thing in the UK before they tried exporting it to America. Presume they're thinking bigger audience/more money, but I'm sure a lot of the rules seem strange to people as it originated from English pool.
