The two donated telescopes were the same diameter as the one Hubble had, but were designed to cover a larger field of view (since the small FoV of Hubble wouldn

The two donated telescopes were the same diameter as the one Hubble had, but were designed to cover a larger field of view (since the small FoV of Hubble wouldn't have been very useful for reconnaissance). But they came without any instruments, so one would have to develop (or adapt the ones from Hubble) to be able to actually use it (and that's were most of the cost is). And the main limitation is quite simply money.. and since a lot of the things that were only possible with HST in the past are possible from the ground now people started focusing on building space observatories for the parts of the optical spectrum that simply cannot be done from the ground (x-ray, far-infrared, gamma-ray).