While Cole may be entertaining, the primary job of the lead announcer of a wrestling show is to get the storylines over, and ultimately sell the product. The viewers have to be able to "trust" what the announcer is saying, in order for the announcer to truly get the storylines over and sell PPV's/tickets/merch/whatever.
A heel lead announcer is counter productive in this regard. By Cole playing a heel role and ripping on the babyfaces, he fails to get the babyfaces over. Cole putting over The Miz makes fans think The Miz is just a geek like Cole.
Eventually, Cole will either wrestle Lawler, or be involved in a PPV match of some type as a ref or manager. Otherwise, what is the point? And after the angle plays itself out and runs it's course, what do they do then? They will have boxed themselves into a corner. Cole can not go back into normal babyface announcer mode, because people will be confused and not believe him when he tries to put over the babyfaces.
It's a fucking mess. The only way this works, is if Cole stays a heel, and they have a new babyface announcer waiting to take over. Which they don't, because they don;t think that far ahead in 2011.