It's like building a structure in the middle of the plains where it'll sit untouched for decades, versus building a structure on the beach where the incessant w

It's like building a structure in the middle of the plains where it'll sit untouched for decades, versus building a structure on the beach where the incessant waves will grind it to bits in short order. Objects in low orbit don't stay there. They're slowed down by the atmosphere, and re-enter in a few months or a few years. Only if they're healthy enough to orient themselves, and have the fuel to do it, can they perform the re-boost maneuvers necessary to overcome atmospheric drag and stay up for longer. So, a satellite which loses control, or gets smashed into bits which can't individually control themselves, just becomes fodder for the drag. It gets swept out of orbit by the wisps of atmosphere out there. Low orbit is very "clean" in terms of junk, because junk simply can't linger there. Just like there aren't a lot of ancient ruins on the beach. The exact degree of drag is unpredictable because the exosphere is subject to a lot of variables, hence the "months to years" ambiguity. But they don't stay out there for decades or millennia, like junk in higher orbits.