Easy: it was going to be a (mostly) closed competition.

Competition gets boring real fast when it is always the same handful of teams. When there are no real consequences to losing, winning becomes meaningless.

Bayern v Chelsea matches stop being as interesting when every game is a Bayern v Chelsea match and most of them have no real impact either way. On the other hand, football becomes most interesting when it's a Bayern v Bremen and Bremen wins. People love an underdog after all, and nothing is more exciting than seeing an elite team take the game for granted and being punished for it.

The Super League is only a more interesting product from the "big name play ball" perspective. It is great when you want to make a fortune in tv rights and licensing, but it sucks for everyone who cares about football as a sport.