#1. Why he won't: Shane McMahon isn't WWE Championship material
Not that WWE hasn't put the WWE Championship on an unworthy superstar before, but the simple fact of the matter is that Shane McMahon is not WWE Champion material. Now you're probably thinking "Well, they did put the title on Jinder Mahal two years ago" and you're absolutely right.
However, the reason for Mahal's push was different. It was to try and secure the Indian market. Perhaps they could have done it, but the way they handled Mahal and turned him from jobber to main eventer in one week prevented anyone from ever taking him or his WWE title reign seriously.
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At least with Mahal, you can consider the possibility that had WWE built him up over the course of 2-3 years, he may have been a legitimate WWE title holder. With Shane McMahon, you can't even say that. He is 100% not WWE Championship material.