The Arecibo observatory shuts down its science.
This looks like the last step in its long decline caused by gradually reducing funding over time: the huge legendary radio telescope cannot be properly maintained, it collapses, there is no money to repair it, and it now, finally, reached its end (there are still other, yet smaller telescopes remaining.). There was a time when there was money to build the telescope. Why did this change so much?
The legitimate explanation would be that this radiotelescope was no longer scientifically interesting, or at least less than when it was built. Or was it a defense project that lost its military significance? Or just palace intrigues over funding? Or something else?