Despite the fact that nowadays even in Enterprise the iPad dominates adoption, because people slowly learned to move on, to forget two decades old tools and are discovering that custom tools, made for purpose and designed for touch input are so much more empowering and productive than running legacy software with a stylus, there's a simple reason for this:
Microsoft has never learned it's lesson. They have been trying for over a decade to introduce new computing form factors and they always based it on their Windows technology and brand. What they didn't realise is that the average consumer (and by this I mean really average technophobe, not the kind of people voicing their opinion on boards such as this) just doesn't care at all.
What people want is beauty, simplicity and easy of use. Power comes though this and not through "raw" power allowing you to run apps made in 1997 on a modern tablet.
IMHO Microsoft also highly overestimates the impact of Office. This might or might not drive enterprise adoption, however the average consumer doesn't give a damn about Office and hence I believe their whole marketing campaign to be flawed. Those people that make decisions regarding IT adoption know about Surface and Surface Pro. Those that don't (regular consumers), certainly won't get impressed by ads showcasing how Powerpoint works. Sorry, that's just not a selling point for most people because they simply have no use for it.
And of course we have a brand problem, I'm not sure why Microsoft doesn't realise this. Windows is huge because of historic reasons, because it still ships on almost all classic PCs sold today and people are used to it for a long time now. However, at the same time I believe when looking at the big picture, there are actually very few people that like it or that associate Windows with something pleasant. Windows does not run on most modern mobile computing devices and people just don't want it there, because in contrast to XBOX, Windows just doesn't really have a good reputation amongst consumers. People hated it on their PCs, people cursed it and people will generally rather say "eeewwwww" than "cool" when you tell them about a phone running Windows.
Despite the Metro attempt to really come up with a "unique" interface, Microsoft has just never had the guts to come up with something completely new and this is what cost them. They have always tried to push their Windows on any form factor and this has lead to nothing but mostly horrible experiences. And yes, even Surface is a horrible experience. We might argue about a few good ideas in there but that's about it.