One of the things that gave it a real sense of scale were the AT-ATs, which act as objectives for the game. If they destroy your shield generators, then you lose. It is for that reason you can't play as the walkers. In an interview with Eurogamer, senior producer on the game Sigurlina Ingvarsdottir explained why it is not possible.
The path? No, you don't. It's a part of the mode itself, because the AT-AT is the objective of the mode. They have a set path because they're headed to the shield generator.
If you were to control their path – that would be game breaking.: Yes – the AT-AT is obviously an extremely unique vehicle. They're so big, their movement is slow, their attributes are so different they have almost their own laws.
I completely agree with this idea. If someone took over the AT-AT and decided to not move to the objectives, your team would lose in this varient. On top of that, and I mean seriously, who would want to play as an AT-AT? They are so slow that their movement would be negligible. No thanks.