I feel like as someone who's been through all the generations of windows as NT, Microsoft has a grand idea for how the desktop should work. It wasn't until iOS came around the corner and landed on the iPad in 2010 that Microsoft felt the pressure to redesign everything.
At that point, surface was a design concept for a table top computer running an application on top of a windows PC. iOS had made the leap Microsoft never could. Rapidly Microsoft turns around a new interface for windows 8 in 2012 and since then we've been dealing with the fact that Microsoft wants to make every computer essentially an iPad ... From 2010.
Everything they do from locking down the ecosystem, enforcing uniformity in design, force all apps to deploy via the store, always online design. This design philosophy was trust into the mainstream by Apple. However apple was right to fragment the ecosystem into Mac os and iOS.
Microsoft wants to beat them to the punch with one OS on everything and it's just not doable without starting from scratch. It's not stopping them from trying.