Aside from what you found out about it being cruel and unusual, therefore an international war crime...

Well, they do have the capability to equip them on hummers, it's just that they are for extremely specialized tasks which are very rare. So rare that none really exist. When would you need one when a .50 caliber can do everything you need done? or an MK-19 fully auto grenade launcher? If it's something that can stand up to a few .50 BMG machine guns, an m134 mini, or an MK-19; you need to get the fuck out of there as fast as you can and call in the drones.

Keep in mind that even though a company like Colt or H&K knows a firearm works perfectly well, they still take years to test the hell out of it because they need to stress test it. Now imagine it's one of the first of its' kind... you don't want to stress it to the point of flushing $3 billion and 30 years of research down the drain.

America made one for soldiers to carry in the late 90s, early 2000s that took 2 men to operate and could produce 2 shots before the battery needed to be replaced. One man operated the actual weapon while the other just carried (barely) the 200 lbs battery pack. The entire system weighed in at ~ 400 lbs. It was quickly deemed super awesome yet completely impractical in every way imaginable. The project was scrapped and the information about it was geared towards what we have on battleships and jeeps today, and one really stupid fucking airplane like the one you mentioned.

A laser works on something like a battleship because a battleship can easily produce enough power for multiple shots. You can load up a hummer/Humvee with one and get quite a few shots off with a lot of batteries loaded up in the back and some other specialized power producing equipment.

But back to my first point; the only time that this would be logistically feasible is if super advanced aliens invaded earth and our already incredible kinetic weapons weren't doing anything against their defenses. If an .50 BMG or 40mm grenade can't put a dent in it, you usually just jump straight to a drone, AC-130 gunship, or missiles from a local destroyer; which do way more damage than a laser ever could/would.