I'd guess:Gonna also put this here: why wasn't this new -100% rebuy mechanic used as the Open Only incentive so many wished for.....?
1) Credits are already available enough for anyone playing enough to get their rank that high that the actual rebuy isn't the bit which costs if you get blown up (especially in a small or medium ship), so it doesn't make for a measurable incentive for anyone who wasn't going to play in Open anyway. I don't think I've ever seen a PG/Solo player whose reason for not going to Open was the potential for PvP state that the rebuy cost was the reason.
2) If, as commonly stated, other players are the only thing which can actually kill a prepared player, the bonus is only useful in Open anyway, so it doesn't matter if you get a 100% discount on your zero rebuys elsewhere. If on the other hand in PP2 there are lots of tough NPC situations to do the same, the bonus isn't a PvP-oriented one in the first place so it makes no more sense for it to be Open only than any of the others do.