When it became easier to use to educated users and more stable and cheaper, all paid server OS’s died.

10b in UNIX revenue in 2012 https://www.tahawultech.com/news/the-last-days-of-unix/

https://cioafrica.co/the-long-slow-death-of-commercial-unix/ one vendor drops from 1.6b to .6b revenue in four years

https://www.matrix42.com/en/blog/2016/10/17/the-cost-punch-of-core-based-licensing-for-microsoft-windows-server Microsoft moves from per processor licensing to per core licensing, to prop up revenue on server OS products. Revenue reported bundles all cloud and software services in with licensing, so any increases in this revenue bundle are most likely attributed to cloud and infrastructure revenues, considering the reported CapEx of Asure infrastructure.

I think even Microsoft is in trouble for OS sales. I have seen an increase in Linux based applications in my industry, at the expense of Windows. SOC appliances are more visibly Linux based as well.