Market share of PHP vs ASP.net market share does not matter in terms of OS as php runs okay on windows. ASP.net can run on linux also but have not tried it yet. However, PHP still has a larger market share than asp.net according to a quick search. This is comes down to the developer preference and which one they like more. Then market share for apache vs IIS with apache but apache is losing to nginx, litespeed, and IIS. Why run nginx or litespeed on windows when you have IIS built in.
Linux VMs run better, at least on xen, then windows without a ton of optimizations and tweaks to make windows run better. Disk IO is one I have seen. Though have not deployed latest windows on latest xen yet (don’t plan to either) so that could be fix with some hotfixes. KVM and other ones may run windows better, but have not looked.
You also have factors such as plenty of file systems to pick from on linux vs NTFS. Which one stands up better against the other in long term deploys. For example, NTFS performance can go down due to fragmentation, requiring downtime a defrag which will affect services. Yes, linux has fragmentation but it is handled better and I have not seen a need for to defrag on linux. Not to mention file system durability against data corruption under loads and unexpected shutdowns. I have not looked at ReFS vs linux FSs, so not talking about that.
And then you get the kicker of Microsoft developing MSSQL for Linux, ASP.net for Linux, and basically trying to be Linux. If Linux was bad, why would they spend the money on developing for Linux? Market share. If the market saw windows as better, they would pick that and plenty of businesses would be researching that.
But what do I know, I am just a janitor. Above statements are copyrighted. Usage of any info provided requires permission and citation of work.