Another reason is that they're only launching one and it has to work perfectly the first and only time it's launched. That level of reliability in a one-off product is incredibly expensive to achieve. With dramatically cheaper launches it would make sense to launch a much larger number of less reliable but much less expensive telescopes.

Another reason is politics, but SpaceX can't solve that one.

What if... SpaceX made up for the pollution they introduce by making the Starlink satellites look up the other way and push the captured data back to earth? The lens and CCD would be small, but with the massive volume (and clear sky) it could add up. Like the amateur set ups using an array of consumer grade cameras.

But those are a special case, air cherenkov telescopes are looking for "less weird" particles like photons or protons. Those can only be seen looking up, since the primary particles moving down focuses the cherenkov light down in a narrow cone.

Basically a big bubble filled with the most useful gas for this + bunch of photodetectors inside at the appropriate places. You could also make the whole detection chamber much larger, than the ~30 km (?) of reasonably thick atmosphere you get on Earth.

https://en.wikipedia.org/wiki/IACT