There are lots of benefits in Windows Os,Some of the Common most popular benefits are :
1. Graphical User Interface : No need to remember lots of commands for working,in fact all the working commands is available in the form of Menus,Tools,Context Menus.
2. Easy Interaction : When we are doing the work,Windows ask us in the general form of different dialog boxes for our response,like "Ok","Cancel","Accept","Retry","Yes","No","Save",simple word for our understanding.
3. Fun Like Activities : Drag and Drop the things from one place to other.
4. Nice User friendly Desktop : its itself says to Novice user to start thier work by clicking on "Start" Button,Choose the Programs from "Program Menu".
5. Mouse Interaction : If something not happen in "Click",Right Click on that Item or "Double Click".
6. Expert User :For an Expert User,Lots of Short cut keys are present for giving input faster.
7. Windows 7 : its a super fast Operating System due to rendering the Concepts of Vector Graphics.
I have given some of the reason,Why do people Prefer Windows?there can be more reasons.