Music recordings made in the 1960s are way different from what we do now. The engineers needed a lot of time to get the sound right at the source and using inline processing to make sure there’s only little to no further processing to be done.
This was before we had DAW. Applying effects once something had been recorded wasn’t that easy nor fast. However, there’s a benefit to that approach. If one properly records so that it sounds like a mix, and mixes so it sounds like a master, one can make their own “sonic imprint” on a production.
Read more about this here: https://theproaudiofiles.com/mixing-as-you-go/