The problem is you'll get certain leagues claiming that their settings are better (vs 343's settings), and you get a big bitchfest of arguments over whether or not that's true. It's just easier for them to say screw it and just let MLG manage the playlist.
A single league shouldn't have monopoly over the hardcore aspect of matchmaking, especially when that league up and abandons the game and shuts out their community from contributing to the playlist.
There should be a neutral Team Hardcore - which is built off feedback from the various leagues and hardcore communities. And since it wouldn't be locked to a certain company's promotional schedule, the hardcore community could actually have their hardcore maps contributed to it, and the playlist could receive regular updates and experience actual evolution from the hardcore community's feedback. This has happened a few times:
Me: That's a nice map there.
Forger: Cool, I made it for hardcore MLG settings. Can I get it into matchmaking?
Me: Well, MLG won't let us submit content for the MLG playlist, but we can submit it for normal matchm-
Forger: *hang up sound*