The radio telescope at Arecibo was once the largest single-aperture telescopes in the world, at 305m/1000ft across. During its lifetime it was surpassed by the 500m aperture spherical telescope (FAST) in Guizhou, China, which is still in use. Interferometry makes "virtual" large-aperture radio telescopes possible by combining inputs from separate radio telescopes. Such as the Very Large Array (US), VLTI, and ALMA, and the planned Square Kilometre Array.
https://en.wikipedia.org/wiki/Square_Kilometre_Array https://en.wikipedia.org/wiki/Radio_telescope https://www.eso.org/public/teles-instr/technology/interferometry/
Can't this do what the Arecibo did, but better?
Yes, and we've also figured out how to mimic the benefits of having a very large telescope by using multiple smaller telescopes that are far apart.
...but why not have two instead of one?
Forgotten about that! China kicking goals as usual.