Punk got huge about a year and a half ago, got the title, then got ignored as champion until he had to drop the title to the Rock. (And he only kept the title so long because Rock asked to wrestle him specifically.) He was never treated as the top guy, and he (like everyone not named Orton, Batista, Helmsly, Lesnar, Undertaker, or Cena) gets virtually no investment from management.
Bryan is a guy who could be big (in a Bret Hart way, not an Austin/Rock/Cena way) and is ready for that push on top, but again, they're not willing to just go with it. Neither Bryan nor Punk fit Vince's vision of what a guy "should" be.