I think the bigger reason businesses aren't updating OS's, is they simply don't need to. Why update something that works?

I'd say 7 was probably the last version where you gained any real benefit from updating. I work for a major company who can run whatever MS software they want, and things now only get updated when the hardware is replaced, and as a company, hardware is now ran until it breaks or needs upgraded. There's no X years renewal policy, as for over 90% of employees, even 10 year old hardware still runs perfectly well enough. However all computers are locked down so you can't install anything you're not meant to, which means they don't get bogged down with rubbish.

At work I've personally got access to a Win7 desktop, and a Win8 tablet. If either were to break today and be replaced with new, they'd come with Win10. When I get a new computer, I simply log in, and connect to the company intranet, then all my required programs get downloaded, installed and configured, and my personal files get copied out the cloud, with no input from me.