Why did the PAC-12 decline in prestige so much in the last 15 years?

I’m a newer college football fan who was doing some reading about college football history the other day. In the early 2010s, the Big 12 seemed to be falling apart- Nebraska, Missouri, A&M, and Colorado all left for what were considered more prestigious conferences. There were rumors before the 2010 season that Texas, Oklahoma, Oklahoma State, Texas A&M, and Texas Tech would all join Colorado in the PAC-12 to form a 16 team superconference. The Big 12 easily could have gone the way that the Big East and the WAC did around the same time. However, a last minute deal with Texas to keep them in the Big 12 promoted the other four schools to follow suit. A&M would end up leaving for the SEC instead a few years later, while Texas and Oklahoma would follow them to the SEC a decade afterwards.

As someone who only started earnestly following college football last year, this struck me as odd. In 2010, the PAC was obviously considered a more prestigious conference than the Big 12. It very nearly developed into a superconference. By the early 2020s, however, it had declined so much that any schools who could secure invites to other conferences did so, including Colorado returning to the Big 12 after an absence of less than fifteen years. Obviously at this point the Big 12 had developed into a better option than the PAC.

Can someone with a better knowledge of college football history than me break down how the PAC fell from a potential superconference to its current state in just fifteen years?