I don't see why they can't do both, have an official website (with RSS), and automatically share the links on Twitter.
Signing up for a Twitter account is free and can be done by literally anyone in the organization.
The answer is because Twitter is easy and free. Self-publishing is neither.
i think the real question is when, not if, we end up with public infrastructure.
The government built the Internet. They can host a website.
Hint: it's not the second one
No change control there either.