Do you mean the asteroids at the Lagrangian points? Every single planet has asteroids there because math/physics dictates those points to be stable. Jupiter has the most at its points because it's the largest planet.
Same with Neptune cleaning its orbit: It has collided with every single thing in its orbit EXCEPT those that synced their orbits to Neptune. An object that is gravitationally dominated by a single planet should not be a planet under any definition.
Sources because I had to read into your claims and I'm no astrophysicist:
https://en.wikipedia.org/wiki/Lagrange_point
https://en.wikipedia.org/wiki/Resonant_trans-Neptunian_object