We've been to the moon and lost interest because we found nothing of value.
That's pretty much it. Space became boring because there was nothing in it for us. Sure, there is likely precious metal and other resources throughout the cosmos, but good luck getting at any of it. At present, reaching the moon is the best we can hope for and getting there and back safely is still dicey. Much less setting up colonies on other celestial bodies.
Take my word for it, this will never happen unless a gold deposit is found. Only then will space travel become interesting again. The television show Ice Road Truckers are not delivering supplies to a bunch of hippies living in peace and harmony. They are delivering to a diamond mine. Unless similar materials of value are found and a stellar gold rush ensues, space exploration will move forward very slowly, if at all. It is too costly and ultimately uninteresting to do for its own sake.
I'm something of a scifi fan, and I think space travel is boring. As boring as regular travel, if not more so. That is simply the reality of it. It was interesting for a while when it was thought impossible. Now that it has been not only done but done routinely, that is exactly what it is: routine.
The current generation has grown to maturity when space travel has been routine and boring. It has not been exciting since the first Columbia mission in 1981. (Or maybe the Challenger disaster in 1986) Since then, it's been utterly uninteresting. Young adults today regard it as noteworthy as the bus. (Despite the Columbia disaster in 2003)
Maybe if new craft had been designed and launched, instead of the same boring shuttle with different names stenciled on them, interested could have been buoyed. But, it hasn't.
Personally, I do not care about the billions of dollars spent on the space program nor do I think that is money better spend elsewhere. I find the space program boring regardless. That really doesn't matter.
Frankly, at this point, the fans of space travel are into it for it's own sake, and anything that exists for its own sake is liable to die an unlamented death when people lose interest.
Interest was bolstered in the 60's with the idea of beating the Russians, but once the cold war ended and nationalism has waned, what kept it afloat? What keeps it afloat for those who care?