Top lane isn't "fine in average MMR" and only a high MMR problem
The reason top lane is queued less in high MMR is because of the lack of impact top lane has on the game (less impact than any other role). Average MMR players are mainly unaware of this lack of impact and think solo lane = carry lane and queue for top lane anyways.
Top lane doesn't actually have amazingly more impact in low elo, it's just a perception difference.