Google, Apple, Microsoft -- they all make money based on closed-source software. What they open-source is only the stuff that does not give them competitive edge. You can't download the source Google Search, iOS or Windows.
(I'm not arguing with you, btw.)
Microsoft promotes stuff like Visual Studio Code and Chakra not to sell Windows - their stand at Node Interactive earlier this month had a 50 inch TV running Ubuntu. Instead, they realise you don't necessarily want Windows, and are happy to sell you Azure (which runs Linux VMs and is a pretty good product).
Most devs beside enterprise IT departments use open source languages for web deveopment. NodeJS/Java/PHP/Ruby/Python/Go are very popular and only a tiny fraction (11%) runs on Windows servers with dotNet or Mono. http://news.netcraft.com/archives/2015/11/16/november-2015-w...
I know if you nmap our website which uses iis it returns as something else because of our load balancer.