#4 He was the cornerstone of the WWE
Alongside John Cena, CM Punk was the cornerstone of the company from 2011 onwards. When you remove one of the cornerstones of a building, the whole foundation begins to shake. For several years, Punk was one of, if not, the main reasons fans across the World tuned in to watch WWE.
He was a selling point of several PPVs, network specials and Wrestlemanias. His name was synonymous with the brand, and he carried the burden of being a top draw excellently. If you weren't interested in Cena's matches, you were most probably excited for Punk's bout instead. He provided an alternative to what the WWE perceived as entertaining.