What happens when you add that much weight to a flat roof and then the snow comes? I'm guessing the snow load is just enough in most cases.
But I wonder if some "maintenance bot" could eventually become established that's designed around the benefits of the regular grid structure. Perhaps "walking" from socket to socket like a gravity-well capable descendant of Canadarm? Wouldn't start as snowplows, but for maintenance tasks at lower frequency, large solar parks could even make very expensive units worthwhile, and from there the magic of mass market might bring prices down sufficiently far.