LEO is not as much of a problem as higher orbits. At the height that Starlink operates unpropelled debris falls out of the sky relatively quickly due to drag.

The greater the surface area the quicker the decay. So if these satellites naturally fall after 3-5 years that means that if they somehow collided with each other creating millions of pieces of debris they would clear out with in less than a year because of the loss of energy during the collisions and the increased surface area.