Claims on frequency bands in orbit are governed by the ITU; because of its international nature, there aren't agreed-upon policies for frequency assignments, so instead the rules are simple and competitive. The first entity to get a satellite in orbit using a specific frequency band gets the exclusive rights to that band, so there's a lot of pressure to get a symbolic bird up early to stake your claim.
You can have two birds share a slot if they operate on different bands (L vs. Ku for example), but there are basically only three popular bands currently in use (L, Ku, and Ka) and using a different one would mean custom designing hardware and negotiating with the FCC and nobody wants to deal with that. Ka is also a bit exotic currently, although it's way more widespread now than it was a few years ago.
This is why some of the biggest satellites we launch are GEO bound communication sats. They're like luxury condos in a high priced neighborhood. Because the land (orbital slot) is so expensive the developers want to make the most of it. Things can be a lot more amateur down in LEO where your freespace loss is so low you can talk to your bird over an omni antenna. There your bigger concern is just getting bandwidth on a usable frequency.
The ISS is actually in a bad position, as satellites tend to go to earth, and the ISS is between earth and most LEO sats (400km vs 600-800km).
Satellites passing through the ISS's orbit do not tend to spend that many orbits there.