Let's look at Saturdays when there was a choice of whether to put a PAC-12 game on ESPN/ABC/Fox or anything else - namely, the PAC-12 networks or FS1. I chose 2019 because that was the last normal national broadcast schedule

Saturday, August 31 - ESPN: USC/Fresno State ABC: Oregon/Auburn (at Auburn) FOX: Stanford/Northwestern
Sat, September 7 - ESPN: Stanford/USC FOX: Nebraska/Colorado
Sat, September 14 - ESPN: Stanford/UCF (at UCF) and Texas Tech/Arizona ABC: USC/BYU FOX: ASU/Michigan State and UCLA/Oklahoma
Sat, September 21 - ESPN: Oregon/Stanford and WSU/UCLA ABC: Washington/BYU
Sat, September 28 - FOX: USC/Washington ESPN: UCLA/Arizona
Sat, October 5 - FOX: Cal/Oregon ESPN: Washington/Stanford
Sat, October 12 - None [Utah played OSU on the PAC-12 networks]
Sat, October 19 - ABC: Oregon/Washington
Sat, October 26 - ESPN: WSU/Oregon
Sat, November 2 - FOX: Utah/Washington and Oregon/USC [4 teams including Stanford and ASU didn't play that weekend]
Sat, November 9 - ABC: USC/ASU
Sat, Nov 16 - FOX: Utah/UCLA ESPN: Arizona/Oregon [Washington/Colorado didn't play that weekend]
Sat, Nov 23 - ABC: USC/UCLA and Oregon/ASU ESPN: Washington/Colorado
Sat, Nov 30 - ABC: Utah/Colorado ESPN: ASU/Arizona FOX: Notre Dame/Stanford [USC didn't play that weekend)

So, the tally was:

Oregon - 8 games
USC - 7 games
Washington - 6 games
Stanford - 6 games
UCLA - 5 games
Arizona - 4 games
ASU - 3 games
Colorado - 3 games
Utah - 3 games
WSU - 2 games
Cal - 1 game
OSU - None

My guess is that BYU would have been on these national broadcasts somewhere between 4-6 times if they played in the PAC-12. That should say all you need to know about the value they bring to the conference. Both BYU home games against USC and UW were on ABC.