the Soviets lost the space race at the final hurdle - despite winning every race along the way with vastly superior technology
You're overstating it a bit. They got the first satellite into orbit. That's significant. They got the first man into orbit because they were willing to risk his life. The US mercury was ready to go at the same time.
So, one clear victory, and then one hair's breadth victory. What did they do after that?
First woman in space? That's not really a victory - that's just identity politics. You could wrack up a long list of those. How about the first left-hander in space? They had the first spacewalk, but that too is mostly just them pulling a stunt. It's not like a project milestone, simply because you can test the suits on the ground.
The first orbital rendezvous and docking is a bigger milestone, in my opinion, than any of the soviet manned program firsts. It proves that you can navigate in orbit (did you know that Buzz Aldrin did the computations for a rendezvous using a sextant and slide rule while in orbit!) and it proves precision control of the spacecraft.
The soviets also had a bunch of unmanned firsts, which they accomplished just by throwing robots and stuff until one of them worked. Same thing the US did, of course. They call Mars the space probe graveyard. Until like 2005 there were more failed probes on the surface than successful ones. But the Soviets got the first successful landing on Mars, and on Venus. I'm not saying that's not significant, I'm just saying they didn't do it with "vastly superior technology."
"Why has no nation, including America, ever returned?"
Isn't the obvious answer, money? If we can't make money, or put our military there in order to protect our empire ...in order to make money, then we don't do it.
Consider the following: In 1970 you could buy a ticket to fly on a giant airliner with more than 100 people that would take you across the atlantic at more than twice the speed of sound.
Why has no nation, including America, ever built another Concorde?
You can weave a conspiracy if you like. Maybe an aircraft that big, going that fast, opens a portal to another dimension.
Isn't it a strange coincidence that the only other aircraft that large and that fast, the Valkyrie, was also canceled?
The Soviets had a program to build one too, but also canceled.
There must be a conspiracy!!
And where are the plans for the concorde? I don't mean schematics. I means construction plans. OMG they don't exist???
This is an easy game to play, but it's not a game that gets you to the truth. Concorde existed. It was real. It was very cool. But there's more money to be made with larger, slower, airplanes. That's it. That's the answer. All the other things (Valkyrie, the Soviets, etc.) those really are just coincidences.
Same with manned lunar missions.
Quite frankly, if Kennedy hadn't been assassinated, the US probably wouldn't have gone to the moon either. It's too hard to keep an expensive project going, and too easy to cancel it. Nixon canceled the last few Apollo missions even though the hardware was ready to go. Why did he do it? Simple: he didn't get any credit for it. And as a politician with an ego, he wants credit! So instead, he set up Apollo/Soyuz - a publicity stunt with absolutely no further value!
After Apollo, the US has
never managed to keep a manned program going for longer than one presidential era. Nova (larger version of Saturn V) - canceled. Venturestar - canceled. Ares - canceled.
The only successful manned program was the space shuttle and the only reason that got off the ground was that the military wanted it (they built a whole launch site at Vandenburg). If not for military support, the shuttle would have been canceled too, and then there would have been no manned space program since apollo. Think about that!
Money and politics are the answers ...and politics is about money. It really is that simple.