My take why Texas has slipped so badly of late:
1) RECRUITING. This is probably the biggest, but it comes down to multiple factors:
a) Texas A&M moving to the SEC. Suddenly they are much more attractive to recruits. Conference games, TV coverage, hype, fan interest, facilities all up.
b) TCU joining the conference, which means another competitive team in conference that entered when it was on a hot streak.
c) Baylor. Baylor was hot as hot. They were getting recruits. They built a new stadium. But they got too hot, fell under the microscope, and fell to earth.
d) Some recruits come in having been high school BMOC's for four years, used to being coddled, and they don't want to put in the effort it takes to be great.
2) Coaching. Charlie Strong seemed like a good hire. Tom Herman seems like a good hire. But these guys have not managed the king-sized egos, scrutiny, and expectations that a job like Texas brings. There are million butts to kiss. Mack Brown was especially good at this. Strong wasn't a popular hire with many of the big egos, so he was going to be on the hot seat with anything less than stellar success. Herman may have a little more time, but days like today won't help. He might be a three-and-out if he loses too many to the Marylands of the world. Everybody hates Texas, so you're going to get their best shot every time (except Nebraska for some reason).
3) Facilities. Texas doesn't wow any more. They've fallen way back with the pack the last ten years. They did a remodel this year to catch up a little bit. But no recruit walks into Texas and sees things they haven't seen at dozens of other programs. Besides, I was never that impressed with them anyway. The practice field is along a busy highway access road, basically under an elevated section of I-35. Really, all of their facilities are average at best considering all the money they have.
4) Home advantage. Or rather, lack of one. Texas fans are fickle. They show up late, they leave at halftime to hit the tailgating. They're not going to stand and scream the whole game. It's never been known as an especially intimidating place to play. Unlike A&M. Those cowboys know how to be a factor.
All this just my humble opinion. So glad Texas lost!!!