SEO text based sites mobile ?

Here I found some some news sites they are only text based, have good seo rankings and thunderbolt page loading speed, they have them on their subdomains (not all)
But when I check the page source code, I could not find out what sort of code that is or which html builder /cms they use.
Are these sites build pure on static html, or with gatsby, laravel, ghost or others ?

Or are these sites wordpress mobile Version of the main site ?
How build such a text based site without using wordpress mobile version/plugins?

check it:

https://lite.cnn.com/enhttps://www.cbc.ca/lite/news?sort=trendinghttps://newsasfacts.com/https://www.nytimes.com/timeswire

I thinks it's possible with google sites ...
But using the same titles from your main site on a separate mobile version (subdomain) is that not double content?