Before co-founding Juriba, I was a Vice President within the Global Technology Infrastructure division at JPMorganChase, managing an extended team of more than 200 people. This was nearly 10 years ago, but I was struggling with the same problem as you are probably dealing with right now: selling an OS upgrade to my business units.
When the time came to talk to our business units about upgrading, I was met with hesitation, frustration, and persistent stalling tactics. As soon as the words "Windows migration" and "PC migration project" came out of my mouth, you could feel the tension in the room rise. I get it. Large migration projects can disrupt or even jar the usual flow of business activities, they require a large chunk of budget and dedicated resource, and the productivity loss and user disruption due to the rollout and initial learning curve can be significant. The downsides can certainly seem to outweigh the benefits, especially if you have revenue generating priorities to balance off against.