Perhaps a realization that the human animal is too fragile and has too short a life span to make space exploration feasible. Weve learned more with Hubble and probes than with manned flights.
The moon project was about Cold War politics, not science. And the science of space is too insignificant to justify the spending of taxpayers money.
But there never was any real space exploration, nor will there ever be.
There was a caveman who once said "we can't cross that mountain, its impossible"
There was some European that said "Don't go West, theres nothing but water and death"
There were people that laughed at the idea of man powered flight
There were people that ridiculed the concept of orbital flight, and making it to the moon
Anything is possible until proven impossible, and proving something impossible is rather difficult.