To show the other side.
It’s similar for us. We also have such a protective wall, and on or behind it various garden waste is disposed of by some property owners. Whether it’s grass clippings, dethatching residues, or the entire turf from the swimming pool excavation.
That may all be natural. But these are sometimes enormous piles that produce smoke and a foul smell and generate a lot of heat. (Spontaneous combustion not excluded)
Of course, the slope is also an attraction for all children and teenagers, and one can only hope that parts of the slope don’t eventually slide away when a child is on it.