Limited by the amount of satellite coverage? Or on the ground limitations from ever greater division of bandwidth? I guess those two are directly correlated, but they could in theory add microwave relays into the mix to help offset higher population dense areas from lower density ones with less used bandwidth.
I think it's mainly a limitation of the beam steering: terminals that are close together need to be seperated in bandwidth so that they don't intefere with each other, and there's only so much bandwidth available. Tighter beam steering could help but that is something that tends to bump up against physical limitations.
(and it's an area where it would need orders of magnitude improvements to address the density of cities, it's not really close at the moment)
In the past I've worked on consensus based protocols like the ones used in modern cellular systems; basically edge devices register with a controller system that then coordinates time slots for distribution/use of bandwidth for the limited spectrum. Adds a lot of complexity and requires highly accurate time synchronization mechanisms to have any hope of working, but they certainly could leverage something like that to further increase support at higher densities. That is, if they're not doing that already.
That's another way to divide up the total amount of available bandwidth (common on any shared medium and they are almost certainly already doing this), but it doesn't increase the amount of available bandwidth in a given area.
You mentioned beam contention as the key problem, which consensus networks solve at the cost of latency at the high end. As for bandwidth, in theory, you get the full network speed when it's "your turn", so that looks somewhat "bursty" when cycle lengths are too high from high demand. Naturally it evens out at human perception timescales appearing as lower bandwidth though. And obviously there's a saturation point where it no longer makes sense to continue slicing the pie and more complex mitigation strategies like exp back off, priority queuing, varying cycle lengths, etc need to be added into the mix.
To decrease that latency in high density areas like cities they'd need to reach for something like terrestrial microwave relays to add more connection points from adjacent (in horizon) "freer skies"
