I find it odd that in the 60s it was deemed affordable, but during the 2 decades of boomer super cycle, the female migration to the workforce, and spending money now which our grandchildrens grandchildren will be repaying... we could ill afford it.
You're missing something important: back in those days, we didn't have to funnel all our wealth to a small number of billionaires (in fact, the term didn't really exist back then). Now, we do. Giving the vast majority of our wealth to a few billionaires like Gates, Buffet, Bezos, etc. costs a lot. So yeah, we simply can't afford this kind of stuff any more.
It wasn't considered to be worth the cost, that's not entirely the same as not being affordable. The US wanted to focus on the Shuttle, satellite reconnaissance and Star Wars.
and ISS and unmanned probes.
The ISS is a good example of this phenomenon - it was going to be "Space Station Freedom[0]" before it became the "International Space Station" because budget cuts made the original plans no longer feasible.
Also the sudden collapse of the Soviet Union, which presented both an unexpected opportunity and a risk. Opportunity in that Russia was no longer the enemy and could be a partner with experience running space stations. Risk in that Russia was not going to spend as much on space by themselves as the Soviet Union did, and their rocket engineers might have been tempted to go work for Iran, North Korea or other countries with nuclear ambitions. By doing the ISS together with Russia, those engineers were kept employed.
Well...there was this whole other "boondoggle" going on at the time in SE Asia that was a black hole for the US's money...