Unfortuately, "low Earth orbit" is a broad term. The article gives a range from 99 miles (about 160 km) to 1200 miles (about 2000 km). Orbits at the low end of that range will encounter significant atmospheric drag and will indead tend to clean themselves up over time (as another poster has pointed out upthread). But orbits at the higher end of that range will not. That's the problem.