The early days of stereo (which is what you’re talking about, the recordings of 70s which aren’t using stereo as an “effect” almost universally have the vocals panned to the center. The old way to take the vocals out of a recording was to adjust how much of the signal present equally on both channels was allowed to be played) were all about two things: backwards compatibility with mono systems and giving people with stereo systems a recognizable effect no matter what goofy system they had.

Wild panning accomplishes both goals.

Studio engineering that used the stereo format to create the illusion of a room or capture the sound of the room the players were playing in wasn’t developed yet and came from the experimental stereo recordings that sound crazy now like silver apples of the moon.