It sounds like a good idea in theory, but consolidating all communities on one instance might lead to some shenanigans down the road. If one group of fans go around and causes the instance to be defederated than all the communities will be blocked.
Also let's say as an example the NFL or MLB does not like what is going on in the instance, they could go after the mods. Example on Reddit was r/NFLstreams was taken down.
I would think it would be beneficial to have league communities and team communities spread out amongst different instances which would make it harder for leagues and teams to interfere with them.
Bloodsport or The Road Warrior.