In the 5 games previous he averaged 20 carries for 129 yards at a 6.6 ypc pace. In the last two games he's averaged 13.5 carries for 53 yards and only 3.9 ypc.
Without doing a total deep dive of game film analysis, it's hard to know if there's been o-line issues, perhaps Bernard has been banged up, or if Houston and TCU simply stacked the box and dared Utah to do anything else. But no matter the cause, they went away from Bernard in both games because it wasn't working for them.