I think this was more of a "panic marketing decision" then a technical decision. RoR was stealing markets every second and MSFT completely panicked, so MSFT felt they had to deliver something which gave them the opportunity to get some of the hype back to "their camp" again...
Also they needed to help their developers gain bac teir self-respect again by getting to associate this hyped word with themselves so that the .Net Developers could look themselves in the mirror again without feeling ashamed for that they didn't know MVC since their platform of choice didn't deliver this kind of pattern for them (out of the box)
For a medium skilled (.Net) developer it's really difficult to not feel like a dinosaur when a medium skilled RoR developer fires up rake and creates a spike in less then 15 minutes having a working and running proof of concept before the .Net developer even is finished starting vstudio.exe... ;)
I guess it's a controversial standpoint, but it's mine and I'll defend it till the bitter end ... ;)
There are countless examples today of that yes, MVC and scaffolding will give you an initial speed boost, yes. But for maintainability, code reuse, encapsulation and mostly every really important thing - MVC just isn't the "silver bullet" and most of the times WebForms are far superior in the long run (unless used like toilet paper of course)