Re: 'All Our Yesterdays' theory
Also, the discovery of time travel could have been a very seductive technology which sidetracked any desire for space travel.
I thought I'd mention that that's the exact premise of one of Isaac Asimov's books.
“A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP” — Leonard Nimoy (1931-2015)