The reason why a lot of these businesses haven't upgraded is because it usually takes years to make this happen.
If you're a business who IT department or enterprise support vendor is running in full ITIL mode with a few ISO business standards thrown in for good measure, it really does take that long.
The amount of paperwork and busywork that needs to go into something as relatively simple as an OS upgrade is something to be marvelled at when you actually have to work in that environment. There are whole massive bureaucracies and months of meetings, followed by change review boards, and more change review boards and testing and more testing and backout plans, and risk registers, and more meetings, and then you have to wait for the next meeting to come along before going onto the next stage.... and and and......
So to all these people saying "just run open source" have never run a multimillion dollar business and relied on Windows to bring home the bacon. Much less have they ever considered being a large collossal IT support vendor that has to maintain SLAs and can get hit for penalities of millions of dollars if those SLAs are breached. These are not nimble organisations. They are not cowboys. They cover all possible failure scenarios and document everything from multiple support networks before they lay a single mouse click on the box.