For one, everyone else caught up with their "strength and conditioning" "program."

They also have to play stiffer competition now. They're in the easier division, but still have to cross over to the likes of OSU, Michigan, MSU, PSU, etc. every year.

All of that results in fewer wins, which results in less attractiveness to recruits.

Keep in mind that they were only in a conference with Texas schools after 1995. Their status as a blueblood was built without Texas and then started to slip after the Big 12 was formed. They kept things going okay under Solich, then slipped a little more under Pelosi, then collapsed.