I have read that the first unmanned landing on either the Moon or Mars, the first thing the probe did was take a photo of it’s footprint, just in case it sank into the sand.
An early 60s science fiction story discusses the problems when a lunar surface tractor with passengers on boards gets “submerged” in a dust-filled loose sea of particles.
Seriously though, why would anybody anticipate “smooth, round, loose spheres” as an accumulated mass when gravity is barely enough to hold the clump together? There is no friction to cause either motion nor wear to break off the tiny bits and irregularities to smooth a surface! And certainly not enough pressure to melt rock.