There were quite a few proposals for how to reuse rockets stages - actually you can see more the farther you go.

Certainly it could have been partially due to not yet having enough experience with many real world launches.

But at the same time a lot of the funding was comming from ICBM programs that don't really care for reuse by design & from army and a high profile space race with USSR. That kinda favored the expensive get-it-done fast expensive MVP instead of a more complex reusable solution that could be much cheaper in the long run.

And then the status quo took root & reusable rocket proponens were no longer taken seriously because - what were they thinkig, this is how we have always been doing it!