Currently there are almost zero incentives for conferences to expand to 16 teams. All you’re doing is spreading out the revenue pie between more teams.
If the Pac-12 ever does expand it won’t be including BYU. Pac-12 expansion would most likely happen because the Big XII is collapsing and in this case they would most likely pick up the powers in the Big XII or get the left over teams such as TCU, Kansas etc etc… which wouldn’t be the worse thing in the world. The Pac-12 gains nothing by adding BYU & only spreads out the revenue from other schools to a school that doesn’t fit the Pac-12 profile in any way.