There was an explanation given quite awhile ago by the BBs about why it's PD and not head-to-head.
If I come across it I'll post it.
Probably one reason is that it is complicated. You can't use a conventional sorting algorithm, since ranking that includes head-to-head is
not transitive. a > b and b > c, does not necessarily mean that a > c.
It would also either require scanning results to determine head-to-head results, or keeping track of all 28 intra-conferences pairs. In the early part of the season, there are lots of ties based on record, but few head-to-head matchups to resolve the ties, so after trying to resolve ties on head-to-head you have to go back to using point differential anyhow.
I would like them to use conference record before points though. I started my first season with 3 games left, and won all 3 but finished in a 4-way tie for 3rd through 6th. It seems that if you are going to classify teams as to which are in the conference playoffs, which are on the sideline, and which conference teams are possibly relegated, that conference record should be taken into account before resorting to point differentials.