Main reason is that lasers don't do as much damage to people as bullets. Bullets poke holes, lasers burn. This laser is for drones and small warheads.

The other reason is that lasers are big and expensive. This laser is mounted on Stryker armored vehicle and probably costs a ton. Bullets and guns are cheap. The regular Stryker carries 50cal machine gun which is overkill for shooting people.

People and bullets are fine for hitting people. Enough that there hasn't been much work in automated targeting. The laser has faster targetting and more accuracy which is good for drones.