I don't now if there are numbers for static sites on there, but my guess is that those numbers don't come close to Wordpress, especially for the top million sites.
> Many CMSs are used to produce static sites; WordPress included.
So, which is it? Don't use Wordpress because it's PHP based and doesn't scale? Or Wordpress headless is okay because the front-end is static?
Static sites are the future, not Wordpress? Or Wordpress is still going to be a part of the headless market because the CMS supports that functionality?
This is an outdated view of how websites are developed today.
> Using a cms to generate static content is much more simple, scalable and cheaper.
If the market agreed with you, then this would be the dominant method for creating websites today. You aren't smarter than the market.
Maybe you aren't looking at the right variables which go into your calculation for "more simple, scalable and cheaper."