Then new UI has to be learned. Nothing is where it was. Various apps probably had to be upgraded too, and they'll have new UI to learn too. Then they have to figure out system administration - how do you do updates, make the funky printer work, deal with anti-virus. I didn't even mention figuring out that whole 32 versus 64 bits thing either.
The time, effort and money involved, especially for small businesses/organisations and individuals is daunting, not to mention a distraction from what their actual business is. By far the easiest thing for them is to do nothing.
Microsoft really screwed up by not making a good upgrade process. They know how to do it, and did it in the past. https://www.youtube.com/watch?v=vPnehDhGa14