Post Apollo
The Shuttle was the obvious solution, after Apollo.
Meant to make space accessible to all kinds of markets !
Meant to send many people up there.
Meant to study the universe, the Earth and the human being.
Heinlein said : once you're in orbit, you're halway to anywhere.
A space station is the first destination. Even before the Moon or Mars.
Unfortunately, there aren't many places to go to and most are so far away they won't be thinkable in our lifetime.
The Shuttle really seemed the best solution.....at the time.