Velocity required to reach a 50 km orbit* above the moon's surface is only ~1.6 km/sec, and there's no air resistance to slow dust particles kicked up by the craft.
For Mars, the orbital velocity is ~3.5 km/sec, thus requiring almost 5x the energy for a given mass of detritus (E = 1/2mv^2); and while its atmosphere isn't as thick as Earth's, it'll definitely cause drag for particles going that fast.
* You don't quite need orbital velocity for a plume to get high enough to disrupt an orbiting craft, but it's a handy reference point.
The lander size under consideration is about 40x that of the Martian rover, I don’t know that a sky crane would work as well without a parachuting stage and atmosphere, and finally it seems rather unhelpful for taking off.
Afaik that's mainly so the plume of razor sharp dust doesn't tear their engines to billion tiny pieces. Unlike the LEM, they won't be bringing a spare for liftoff.
