Group mid, no problem. Group top with mid and bot inhib down, impossible to achieve. Why?

Note, this is silver-gold elo, depending on factors. But I am finding it almost impossible to get people to 5 man top if the other 2 inhibs are down. People muck around in botside jungle, try to push mid. All sort of things that seem fine if we are trying to push for mid turret, but we are past that.

Anybody know why this is or how to motivate a team to group for the win anywhere but midlane?