Re: Higher was better
It might be that the existing mast is in too good a position. If you have more masts but with smaller coverage it means you can handle more users, otherwise sticking a cell on a very good position might go too far. Too many users per node.
Possibly the owner of the existing mast might want too much money to site their equipment, and/or not have enough electrical supply or telecom capacity to service it.
The best locations have already been used, it's been a long period of filling in the gaps and there are still a lot of them.