Those 60s Bond singles - not quite the same?

The most marked is Nancy Sinatra's You Only Live Twice, which I bought as a single though I have it as album track. That was just an indulgence, though it's been argued on the vinyl thread that singles sound better than album tracks, on account of having more space to devote to the sound.

But this version lacks the lush Barry orchestration. It has a raggedy electric guitar and sounds a bit lo-fi. There's a case for doing a groovy version of YOLT with those funky bass guitars or something that feature on the soundtrack itself sometimes, to make it a bit Austin Powers, but this isn't it and it's a bit disappointing.
The B-side called Jackson is a C+W tune, quite famous and rather good.

Then I get the single of Goldfinger. This does have the orchestration but is still not quite the same as the one we all know. Bassey's vocal take seems different, a bit more improvised and off the beat. Not bad but not the same.
Again, the James Bond theme single is v similar but spikier and punkier, livelier and less stately than the one we know, even though it was surely released at the time of Dr No.
What gives? Why do they do this?

Was it for some kind of copywrite reason that the single is different?

You get this stuff on other releases. A John Barry collection doesn't have the same Tom Jones version of Thunderball, it's a bit more rock n roll, less lush, same for the version of OHMSS.
The vocals for TB and YOLT were not even allowed on the brilliant 1971 release, The James Bond Collection, which spanned Dr No to DAF.