You just explained why they didn't reset MMR. Those that got Glad are the only players that would. If they reset MMR, the same people would still end up getting glad overall.
Gear levels are low, but that doesn't mean they make players bad. If you have a good set of players / team, you would face roll all the "lower" rating players anyways.
Until there is a rating decay, the same teams will either win trade or just sit at a high rating and camp getting Glad.