everything is 2.5D - it’s 3D, but all movement is on a 2D plane. There were lots of issues with things not looking like they are lining up (because they weren’t, since we do some strange things to fake this 2D behavior). The lasers would be an actual object, whereas muzzle flashes and bullet tracers are particles, making this slightly more complicated. It was so long ago, I don’t remember all of the details, but that was one of the major reasons.
edit: I should add that there are a MILLION features like this we wanted to add. But we’re a small, indie studio and at the end of the day, we had to make sacrifices in order to ship the game. It’s easy to point to one and say “that’s easy, why didn’t you add it?!” - but you have to remember we don’t all have Blizzard budgets and time frames :]