Laser tanks are impractical. What if the enemy wears mirrored shades? That laser goes right back and kills you instead. You don’t want your 100 million dollar tank to be taken out by a pair of Ray-Bans.

Mirrors melt and break when hit with a laser of more than “pretty lights power”.
This dude built a 2kW one with optics: https://www.youtube.com/watch?v=xNmbvaUzC8Q
mirror at ~ 4:30

EDIT: I know where I am, that video is too good not to share though. Vote away.