He made a lot of bad decisions in recruiting that resulted in Texas going from being the #1 destination in state for talent to losing their edge under Mack. His best years came before the rise of Gary at TCU, Baylor was nothing, A&M had lower ambitions, and fewer outside programs were poaching Texas talent. That all changed as Texas began fall from grace under Mack, they lost that talent and then they started losing the games. Gotta wonder at this point if Texas can ever be top dog again at this point. For all the money they throw around it hasn't done much for them lately.
This isn't what happened. Mack was known for putting a border around TX and locking up the in-state talent even near the end of his tenure. He probably did the best job of keeping talent in state of any coach in the country. Most of his recruiting classes were locked in very early. If he made any mistake recruiting-wise that may have been it. He probably would have been better off waiting on some of those kids to see how they performed their sr. years and recruited more nationally. Still, that wasn't his biggest issue either. His biggest issue was he lost his coaching mojo and he stopped competing for and winning Big 12 Championships. It's as simple as that. From that, the team developed a poor locker room culture, and after 16 years, UT finally had to let him go in 2013.
In 2012, UT had the #2 rated recruiting class - 28 total recruits, 25 of which were from TX. The previous 3 years were ranked as follows:
2011 - #4 (almost all from TX)
2010 - #2 (almost all from TX)
2009 - #6 (almost all from TX)
TCU, Baylor, and A&M didn't even crack the top 15 recruiting rankings any of those 4 years, and only A&M cracked the top 20 when they finished 16th in 2012. UT didn't lose talent to any of those programs.
Mack's final 3 years or so were spent with his butt firmly on the hot seat, and when he started losing again in 2013, the writing was on the wall, and recruiting finally took a hit - #17 recruiting class which is somewhat typical for top-tier schools when they fire their coaches.
Mack has always been one hell of a recruiter. He just isn't as good at developing a program as he used to be.