Probably intended for stereo and mono recording, back in the early days of stereo when somebody thought a stereo vocal was a keen idea
or perhaps they couldn't decide which mic would make her voice sound the "best" so they used three and decided which track to use later? or is this a silly hypothesis?
Considering the recording technology of the time, I doubt they did that. Maybe, it was possible, but most recording was to mono, stereo or 4 channel. 8 channel existed but wasn't common. Remember, Sgt Pepper was recorded 4 track.