I'm assuming you've never played Planetside, which actually had mechs in it. They had customisable weapons and so on and were generally the most hated feature in the game ever, because they rolled everything with no team required. They were the reason many, many of the subscribers left the game.
The problem was simple. A single guy spawned himself a BFR and voilá, not even an entire coordinated team could bring him down. That's not good in a game about coordination and many players and is also
one of the reasons Planetside 2 isn't the best FPS game ever made (as it threw these concepts through the window and instead went for BF-esque vehicles and mechanics... which are designed to compensate for the small number of players on the battlefield compared to RL where the machinery itself requires those 32 people to operate).
Edited by Adridos, 20 October 2013 - 01:13 AM.