The only thing I can think is that RR is brutally honest with these guys. Guys are not seeing the field because of seniority, they earn their spot on the field. He has incredible expectations from his team and it appears a large number of them, but not all, are willing to give it their all to reach his expectations.
For those who can not or will not put forth the effort required to play on game day, a transfer is an easy solution. Every one of these guys dream of playing in the NFL. That dream may not be realistic, but it is still a dream. I' never going to hook up with Jessica Biel, but it's still a dream.
If a player realizes that he's never going to even see the playing field on Saturday, some of them see the solution as transferring to another program. Thank God for guys like James Rogers who decide to rise to the occasion and get better.