[loudist]

Back in those days, the recording technique was to compress or limit every instrument going in on the tape in order to keep the recording level persistant and as close to zero as possible.
This was done for improving signal to noise of the tape formulations of the day.
The sonic component of compression was not the reason for doing it but was a 'benefit' anyway. It also made doing those pre mixes a lot easier.
This is a very large component of the character of the sound.

Also, usually during a bounce, there was an instrument being recorded live along with the bounce onto the bounced track along with the others off of tape.