This 100% I Saw an interview with him at the start of the offseason where he said when he came back the offense had changed. He said something about it bothered him and he needed to adapt. He took all the blame and kudos to him.
I think it's 3 things, 1) he is used to being the focal point in sports and that ain't happening here. 2) as Steve Smith said " everyone works out at this level". He wasn't going to be able to just come in and bully NFL DB'S. Hopefully he put on size and strength this offseason. 3) it's as McDermott pointed out, he didn't approach his return like they wanted him to. I that as a combo of 1 &2.
Look no one wants the kid to fail,but so far it doesn't look good when you see how BTJ, and McConkey have performed.
Now as I said,the kid in his interview seems to have gotten it,but he has to prove it on the field.