I'm probably not gonna going back and watch games to corroborate (a.k.a. possibly talking out my ass), but I think teams are getting better at defending Morgan's bread-and-butter slant RPO by parking LBs and/or safeties in the slant passing lanes and forcing Morgan to throw to the sidelines or deep. Plus, defenders have had success by stacking the box and successfully blitzing off that which forces the Gophs to go with heavy packages which then limits the offense to 2-receiver sets thus limiting pass route options. I think this is why we've seen more TE catches this year.
Side note to this, the Gophs may be doing more heavy packages because that's where they have a lot of talent with less talent at RB with Mo out. Mo could get his own yards against stacked boxes without extra lineman where the current young RBs do not. We're not going to see the 2019 offense this year. This year's team has not had that level of WR/RB skill on the field, but arguably has better talent in the O-line and TE for pass catching. It's taking some time for the coaching staff to find that groove with the current talent.