everything is not as it seems

Not all weapons that are called lasers are lasers in the sci-fi world. For example Turbolasers in Star Wars are actually a high energy plasma cannon. The plasma cannon has recoil because it is shooting out something physical. "Laser" is probably just a hold over term from some point in the galactic past.

As for the neutron cannons, the recoil may be because the neutron is the most dense part of the atom. That s really just a guess though.