Why doesn't the military do this? are they stupid?

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.

We can put shades on the tank to bounce it right back
- WAR… is.. disco?
  Next your gonna tell me the raving rabbits are the ones driving them.
- What if they do this
- Doesn't that cause a nuclear explosion?
That's when you go back to explosives, you don't even need shrapnel anymore, they are already wearing it!
The moment those mirrors stop being perfectly shiny they begin thermal collapse. Which is the real reason mirrors exposed to the atmosphere can't be used as targeting optics.

Counterargument:

I only we had something we could fire that do almost the same arc as that. That would be ballin'! So I'd call it ballistics

Ridiculous! You would basically need the mass of a planet for that to work.
- Dangit! We won't find that anywhere on Earth!
That would work if the earth wasn't flat. As it is, you need to transport the artillery below their position and shoot them from there. Like Ender shooting through the ice clouds.

the tank is confused by its own reflection and attempts to fight itself

This is why certain Army weapons are not appropriate for the Marines

If you fire a laser against a mirror, it bounces but raises the heat of the mirror so you end up melting the mirror and destroying the drone.

I may risk being too credible here, but a $80 drone is a lot more expendable than a $40m laser tank. The drone can be considered a consumable. Hell, mark the drones down as ammo.
Depending on how long you do it, how powerful the laser, and how quickly it can cool off at the same time.
And like the other guy said, you can make really good mirrors if you only care about one wavelength.
But the drone stays in the air by making wind, which would cool down the mirror?
- Unironically yes. If that's not enough, add water.
not if you have total internal reflection
- In all seriousness, wavelength-specific dielectric mirrors can approach six nines of reflectivity.
  The hard part is hitting the mirror instead of the drone.

Sigh.

Because good lasers are red.

...the color of a blaster bolt (character-scale or starship scale) is determined by the quality of the gas used in it - higher quality gives you green, lower quality gives you red. The Rebellion didn't have access to the highest quality gas, and had to make do with the lower quality ammunition.
Huh, I guess I wondered but never looked it up until now.

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.

I rarely give my time to videos that long, but it was awesome for the full half hour. That guy's having fun. Thanks for sharing.
- It's very important that we give him views before he kills himself doing a YouTube stunt
Nah. This doesn't count because that guy is clearly from the future when you can buy a 1K laser at the corner store. In 2024, they are a little bit harder to come by.
- Uhh, wut?
I actually studied laser physics in university and still learn a ton of practical shit from styropyro videos
This is the most fascinating thing I've seen on youtube in a long time.

We don't need Sky Ranger, mirrorbois or lasertank, we have shitballoons.

Buddy called inverse-square law

Inverse square law is just a geometric limitation, focus your lasers more, problem solved.
- "You see, men, the lethal range is limited by this airy disk... stop giggling!"

This is also how you check if your ass is clean.

Laser artillery!

Queen of battle! Yasss

This was a real concept for the anti-ICMB 747. The idea was to loiter it outside air defense range and then send drones in as reflectors to target the lasers much closer to the threat.

Interesting! Yeah, I think in the right atmospheric conditions this could absolutely work.
Why it's NCD, as drawn, is that shells already exist and do exactly this when fired on an indirect arc.

Alternately, polish every car window facing east.

Or... skip a step. Line of sight is irrelevant if your aircraft is already exploding!

There's a building in central London that melted a car. Solar laser, so SEO friendly, so on fleek.

I actually do this with my TV infrared remote control.

Because Still Lasers aren't lethal, duh!

Porque no los?