Geosynchronous orbit is a Very high altitude. It’s 6% of the distance to the moon. Inverse square law tells us the surface area that we have to worry about for debris is massive compared to lower altitude orbits. Additionally, it takes a lot of fuel to be able to de orbit high altitude satellites. As orbital altitude increases, de orbit costs start getting out of hand and there is less benefit to deorbiting. So while lower altitude, crowded orbits are required to de orbit to avoid catastrophic cascades from collisions, higher altitude orbits are allowed to simply get out of the way.