My theories on why Pac12 fell a part. (I think it is more than just Larry Scott);
1. Poor Financial Decisions (Pac12 Network) - I am not going to explain, plenty of sources out there that explain it better than I could but this was notable one. Larry Scott seem to drive a lot of these errors. I want to get into some of the lesser known reasons.
2. Changing Dynamics in CFB - Arms race with B1G and SEC for relevance which is also driving the collapse of ACC and diminishing of Big12 with OU and Texas leaving. Big names are consolidating into two leagues (it may one day be a single league)
3. Lack of Football Programs on West Coast - This is something new that I want to add. It is a BIG reason for the Financial problems and perhaps diminishment/weak branding on West Coast.
I made a post somewhere that California has about as many FBS teams as Louisiana (7 for Cali to 5 for Louisiana). The Pac12, as a result, has been geographically spread out. USC going to Oregon or Washington is the equivalent to Tennessee going to Minnesota or Boston College from a geographical standpoint. SEC teams are just a lot closer than Pac12 teams. SEC teams also have far greater option for games. Take LSU, they can schedule Tulane, UL Lafayette, UL Monroe, Houston, Baylor, TCU, Arkansas State, Southern Miss, UAB, Troy, Memphis, and MTSU OOC within the same range as USC only being able to schedule San Diego State OOC.
Pac12 teams have had to travel a lot for OOC games as a result (along with Conference games) resulting in more difficult travel for fans and more financial strain. SEC had two Power Conferences and three G5 Conferences on their door step. B1G is in a similar position.
This also made expansion for Pac12 very difficult as they didn't have many candidates unless they added teams far from their epicenter. SEC can add teams in neighboring states such as Oklahoma, Texas, Texas A&M, or even schools like FSU, Clemson, UNC, Miami, etc. and improve their league. Who does the Pac12 have other than traveling to Texas? Their options are a lot weaker with BYU, UNLV, Boise State, Hawaii, Fresno State, San Diego State, etc. Not the same cache as available to SEC or B1G with expansion.
4. Diminishing product on West Coast - Some of this is impacted by #2 and #3. LA, San Francisco, and Seattle are primarily pro sport cities with USC getting some attention in LA at times. The culture just doesn't match that with the B1G and SEC. SEC likely benefited by not having Pro Sports teams until very late in the game so loyalties grew up with a college focus. Even today some states (such as Alabama) have no Pro Sport teams. The Atlanta Falcons, Jacksonville Jaguars, New Orleans Saints, and to a degree even the Tennessee Titans live in the shadow of their local College program.
Pac12 also hasn't competed often at top level of Football and their stronger teams lately are far from the population centers (Oregon and Utah). USC struggling actually hurt the league and its brand.