The Power 5 are wanting to play only Power 5, and two of those conferences PAC-12 and B1G want everyone to play the same number of conference games. The number of conference games is either all Power 5 conferences play 9 conference games or 10 conference games which would exclude conference title games. If the Power 5 all play they same number of conference games it would help figure out who should be in the playoffs.
Why would the Power 5 or any conference if the FBS want to add another conference? The FBS is at 10 conferences which makes dividing the bowl money evenly amongst the conferences (I'm sure the Power 5 get more money from the bowls then the G5). So let's say the Big Sky gets added to the FBS, the bowl money that the Big Sky would get is going to come from somewhere. Those other FBS conferences are not going to want to loose the money that they'd get to the Big Sky.