A few major issues:

• Air absorption. The extinction coefficient for free air is ~0.012/km for 500nm light (green) at sea level. Or about 50% losses at 60km. (Now, this is well above sea level. Still.) Both for direct power losses and for secondary effects (high-power lasers have a tendency to create an ionized channel. Natural lightning produces a surprising amount of NOx and O3, and widescale power beaming would too). (For comparison: HVAC lines lose ~7% / 1000km. Or ~0.000072/km. Or 50% losses at 9500km. More than two orders of magnitude better.)
• Conversion efficiency.
• Beam dispersion in general.
• Malice.
• Accidents.
• Energy cost of the fliers themselves.
• Speed of said fliers.

I could see this working reasonably well for defensive warfare (until the power generation gets nuked); this is hilariously ineffective for the stated purpose of long-distance power transmission.