According to George Martin (in his autobiography "All You Need Is Ears"), the panning was a mistake.
Those early records were meant to be mono mixes, but they were recorded on a two-track machine. EMI hadn't gone 4-track yet. Then some idiot suit in LA decided they could make them "stereo" recordings, which at the time were just catching on and fetching a premium price. Martin only became aware of it when he heard a song on the radio on a trip to Los Angeles, and was quite dismayed.
By now, we've come to think of that goofy effect as how they are supposed to sound, and any remixer would feel obligated to preserve it in the name of "authenticity".