@frost I have to agree with Genobee. Saying that makes no sense at all as you can actually have much better control with WASD or Controller Support when it comes to speed/aiming then you can trying to juggle movement and actions with mouse only controls. In fact his reasoning with POE is sound since you HAVE to give up a skill slot for movement in that game else risk basic attacking any enemies you want to move around.
@Genobee is looking for a real reason which can honestly range from balance reasons (because it can make a difference just like 3rd vs 1st person mode) or could even be a coding reason as it is just easier to stick with one style.
No idea what their reasoning, hopefully a developer responds.
Personally prefer WASD myself, but the game matters more then the controls to me.