No, it's even more simple than that. Mazi has a horrific habit of standing up at the snap. In doing so, he loses the leverage battle. He got away w/ it in college, as he is so strong he could manhandle most OL's even w/ this technique flaw.
Now, though, he's in the NFL where everyone is strong. If he ever corrects this flaw and stays low, he will be pushing the OL back into the QB on a regular basis. He has the strength to do so.
Hard to say why it's not corrected. He might be stubborn, but in all likelihood, it's just a matter of reconditioning his instincts. It's very hard to relearn something after doing it wrong for his entire career.