I'm just speaking personally. I just think it's harder to produce success like that.
It also depends what your making. I think if you're looking for a creative, new idea, then that's more challenging than making a racing game, which is arguably much more formulaic. The core principles of a good racing game are established, the core principles of x unknown innovative game are not.
Additionally, I think Microsoft have inadvertently placed a lot of pressure on this new studio with the reveal. Which can be difficult to deal with, and they may struggle to manage the expectations of consumers.
I'm hoping, but perhaps this is unlikely, that they'll start by producing smaller games and slowly expanding. Consider how Media Molecule started with Rag Doll Kung Fu, then moved to LittleBigPlanet, for example. Scaling the growth of the studio and producing deliverables that can act as a metric for success reduce risk and help manage realistic consumer expectations. This is also what Sony did with Evolution Studios, where they scaled the studio back and then encouraged them to produce Motorstorm RC. It helps the team build confidence and develop a workflow by engaging with a lower risk project.
Even seasoned developers like Bungie, who left Microsoft to strike out on their own, struggled internally with the development of a huge, triple A game. It's not easy, even for a highly experienced team and it's considerably more difficult when everyone is working together for what likely is, the first time.