Kind of odd that nobody could explain it.

Did you read the Wikipedia entry you linked? The explanation is incredibly convoluted. No wonder nobody can explain it. I just read it, and I couldn’t explain it to someone. It seems like the reasons were logical when it started, but when I had that number in the 60s, making a call was essentially the same as today (except no push buttons), and there was no reason to keep up with those two letters at the beginning. It was just a holdover from the olden days, like Daylight Savings time. We tend to be reluctant to give up old traditions, no matter how pointless they are.