Jason Craft... Why does he get toasted so much?

Apparently he's been struggling with biting on fakes and such for a long time now. Why doesn't he respond to the coaching. They have to see what he is doing wrong. I just don't understand why they give him so many chances.

Does anyone know if DeLoach is any good? I like his size, but can he cover? He is currently listed 4th on the depth chart behind Groce.