[edanm]

Writing using authoritative language is very common, and widely considered a best practice.

I highly recommend you simply accept it as what it is: the way some people communicate, especially online. It's not worth your time/attention/care to think about this.

[raverbashing]

Yes, you're right

But it still looks like they pulled some rules out of nowhere and are enforcing them.

[pifflesnort]

Writing 'authoritatively' is used as a pop-culture substitute for reasoned argument. I find that it's a good litmus test for determining who I should ignore.