Even in 2017 they were 32 (s&p). 7th in 2016. It hasn't been a trend. It was just this last year. Before that it was the passing defense that was worse, like 2017.
They need to spend and ENTIRE off season running a certain defense. This last year was much less about how the LBs themselves performed and more about what it was coaches were having them do. You play an inside LB way back and he meets a RB going full speed 3 yds past the LOS. That can't happen. They have to decide on what the heck they're doing defensively.
Not saying the players were flawless. They had their share of issues and there was a lot of youth. BYU needs more off-season contact to help with that, and they need to get them in the right system.