Most people dont even use the operating system. They look for the apps menu, then click what they want to run. Most people can switch between OSes easier than you think because there really isn't that much difference in how they work on the surface.

users are one component, but you are still ignoring/forgetting the rest.

user management, file management, security, windows-specific software, auditing requirements, required capital investment, lack of competent linux sysadmins compared to windows sysadmins, and so on.