Not too long ago, a lot of Customer Relationship Management (CRM) software ran on MS SQL Server. Businesses made significant investments in software and training, and some of them don’t have the technical, financial, or logistical resources to adapt - momentum keeps them using Windows Server.
For example, small businesses that are physically located in rural areas can’t use cloud based services because rural internet is too slow and unreliable. Its not quite the case that there’s no amount of money you can pay for a good internet connection in rural America, but last time I looked into it, Verizon wanted to charge me $20,000 per mile to run a fiber optic cable from the nearest town to my client’s farm.