* https://docs.github.com/en/packages/working-with-a-github-pa...
https://www.reddit.com/r/webdev/comments/lg9xnm/why_do_some_...
Same with local governments. They love something really random like <countyname>proptaxpayment.org instead of treasurer.<countyname>.gov. It's exactly the kind of domain you are told to watch out for, but actually legit.
It does not seem to hinder e.g. Google using google.com, youtube.com, gmail.com, and several (many?) others to collect your data. Do you say security and privacy work differently here?
In the case of user data domains, intentionally in the design of the service or via a security hole, users may be able to execute code and read cookies (e.g. in JavaScript on a page hosted on githubusercontent.com) and that's undesirable.
The local government itself may have an IT department, but they may not know how to create a subdomain, or even be aware this contract is being made and the site is being set up until after it's announced to the public.
But if the different domain name gives good protection / isolation, why does Google still use completely different domains for different services with content controlled by them. I cannot believe they are interested in protecting users from data collection.
JFTR, I also think they could at least have used a couple of pronouncable domains, or put stuff under a .github.io domain, or at least make it githubrepo.com or something not acronym-y