It's not just Nadella! It's a cultural war inside Microsoft, and goes all the way back to the 'classic' Visual Basic vs. .NET days.
On one side you have the 'Raymond Chen' school, who understand one of the main strengths of Windows has always been backwards compatibility and how important that is. In his blog Raymond tells that when Win95 was being developed, Microsoft bought a truck (literally!) of different software from a local shop and distributed the packages among its developers, so they could look for any incompatibilities and fix them before Win95 shipped!
On the other side, you have the 'we have no common sense' and 'new is always better' school. They want to get rid of everything they consider 'clutter from the past' and start from scratch, not realizing that the 'clutter' is there for a reason and is, in fact, the glue that keeps everything together. They are ideologues, and therefore have no common sense or even care what happens IN PRACTICE, nor how much suffering the full consequences of implementing their ideas will bring to others. It's not their problem and they think it's perfectly ok to bring people kicking and screaming into their utopia - they are doing them a favor, after all.
It's somewhat amusing - if it wasn't so sad and alarming - to see that what is going on with our society these days was already being reflected inside Microsoft over a decade ago.