Different orbits. For two things to collide in space, orbital height (altitude) has to intersect. And the orbital parameters of anything up there is tightly controlled/regulated.

Plus, the thing about space is just that: There’s an awful lot of it. Even if two objects’ orbits do intersect, the timing has to match as well. Two objects can be on the same orbit, but out of phase with each other.

And since this is three dimensional space over a globe, the higher you go, the more room there is.