I wouldn't think there are many use cases for Windows, but I imagine supporting legacy .NET Framework apps would be a major one.
Is there any limitation in running older.NET Framework on current Windows? Back when I was using it, you could have multiple versions installed at the same time, I think.
You can, but there are companies that also want to deploy different kinds of Windows software into Kubernetes clusters and so.
Some examples would be Sitecore XP/XM, SharePoint, Dynamics deployments.