Beam power and the related time-on-target pointing requirements could be thought of as the laser weapon equivalent of the rail gun’s rail erosion problem, a possibly show-stopping barrier to an otherwise attractive concept. Something simple as programming the drone to make erratic movements which constantly alter the presented aspect can vastly increase the tracking/pointing sophistication needed to maintain time on target, and compensating with increased beam power rapidly hits practical limits, particularly for an airborne system.
Still, countering relatively unsophisticated drones is a major Israeli objective, and it does appear they are close to a system that would be at least somewhat effective at that.