Well, web formsWebForms have more learning resources available (simply due to the fact that it's older) and thus new programmers that aren't "In"in the know" will be more likely to find information regarding this older technology as opposed to the newer stuff like MVC.
Senior/experienced programmers are older and will be more proficient in the older technology due to the fact that they've programmed in it longer than they have in the newer one.
Unless you can spend the money and effort to get your guys as proficient in MVC as they are in web formWebForms applications, youryou're undoubtedly going to try and hold off upgrading to the new platform for as long as possible.
So it presents several logistical problemproblems: Do the benefits of MVC outweigh the it's cost in terms of lesser quality and deployment time? If I have a site written entirely in webformsWebForms, would it be worth the effort and money to integrate MVC into it?
As stated by a previous commenter, MVC also prevents you from achieving the same level of interface with the controller as you would be able to with web formsWebForms. While I'm all for the "Keep the user from fucking shitstuffing things up/learning" side of things, it can still be unreasonableunreasonably troublesome for teams to deploy/implement a program that fanatically sticks to that paradigm for everything they write.