Microwave beams are attenuated in heavy rain. Typically, the beam is not going through heavy rain.

The 60% over a kilometer is not due to atmospheric absorption, it's due to losses at the transmitter and receiver (and beam spread exceeding the size of the receiver.) If microwaves lost 40% of their energy in a kilometer radar would have a hard time working.

Millimeter waves are more strongly absorbed in clear air, so they are not as good for this use case. They may be good for powering aircraft.