WWE can be pretty selective at times when it comes to injury prone wrestlers. Sheamus is constantly pushed or kept near the spotlight even though he's just as injury prone as other wrestlers. Same for Orton and Cena in recent years.
Bray pretty much has Barrett-style bad luck where the injuries are happening at the worst time and almost always as some sort of fluke accident. If Ziggler was positioned better during the roll-up, Bray doesn't twist his ankle and jeopardize whatever plans they had for him at SummerSlam.
Link to the recent Bray injury since the gif itself is pretty large:
http://i.imgur.com/8gBQcMC.gif