Scaffolding is the old way to reach a facade. It works, and it also takes time to build, space on the ground, and people working at height.
A cleaning drone reaches the same kind of surface from the air. The pilot stands on the ground. There is no scaffold to put up and take down, so many jobs fit in a shorter visit, and the entrance stays easier to use.
It is not magic, and it is not right for every wall. Very delicate stone, or a site with no safe place to fly, needs a proper look first. That is why we ask for photos before we set a day.