Applications – How does the download of apk websites work?

I'm curious and I'm worried that my apk is the country
Restricted is downloadable from a website, for example
It is also not Google's responsibility to restrict the download.
of apk in countries that are restricted by any means. I only want
know how these websites get the playstore apk and they also have
All previous versions of the application.
link ..

Please, give me something brief about it.