Jacobs has said in many interviews that he wanted the mask to come off. He was tired of it and he thought in his opinion it was holding him back. The heat etc was annoying and that is why the mask started to get smaller. Also, it didn't help he can only see out of one eye, so his vision was also a problem with the mask.
I for one miss old school Kane with the mask but it was a time that i enjoyed and never will forget.