I would say fairly often it happens where a kid is expected to get some time. He travels for the first few series and doesn't get in, then the kid gets a nagging injury like a sprain or arm problems. Next thing you know you're 25 games in and he's not going to be 100% or get a ton of meaningful appearances so he gets told he's being redshirted halfway thru the season.
Redshirting isn't the end of the world if there is an everyday starter in front of you or some nagging injury that will prevent you from being at 100% everyday. You probably could play, but does it make sense to waste a year of eligibility on 6 ABs one weekend for you to be shutdown for the next 12 games? The redshirts I see transferring were the guys who didn't belong, or the guys who are very talented but caught up in a positional logjam.
It is one thing to be redshirted and not see a future. It is another for it to be circumstantial. Personally I would rather redshirt than get 9 ABs in midweeks over the course of a 60 game season.