Lbs and safeties are more athletic and better able to cover the middle. Offenses prefer quicker slot WRs. Of course there are some exceptions to this for some teams with great TEs.

Holker was being used and was third on the team in receptions at the time he quit. That’s about average, and he would have likely been the starter this next year, assuming this is Rex last year. One thing I didn’t see from Holker was an ability to use his body to go up and get the ball. Specifically when they tried him on sidelines routes. He showed some great hands on crossers.

You may notice that BYU asks their TEs to block more and I think Holker didn’t like that role. Plus obviously BYU has some great WRs who are tall that took away some reps. As did Rex.