#3. Why he won't: Doesn't want an authority figure to be WWE Champion
Which other authority figure in WWE history became World Champion? Vince McMahon himself. And mind you, it wasn't just the one time - it was twice, technically speaking. He won the WWF Championship during the Attitude Era and also won the ECW World Heavyweight Championship in 2007 during his rivalry against Bobby Lashley.
Of course, the whole objective of the latter title reign was to put Lashley over (something that Vince McMahon has undeniably been selfless in for many years), but he likely wasn't a fan of the idea of being champion himself.
Of course, the title reigns were short but he knows from experience that having an authority figure as World Champion doesn't really help the product very much. However, that doesn't mean he won't do it, but he does know from experience.