The goal is for wordpress users who self-host to not post here but to instead post to .org
So a self-hosted user has a problem. They do not click the links in their blog and instead go to the .com site. It's like me going to playstation.com, apple.com, microsoft.com, most-sites.com
They make no connection between the software they use and the forum they arrive in.
If they have not come here before then how will they know it's the wrong place?
You are asking them to make the connection between their blog and 2 sites they have never been to before. And given the nature of sites it's natural to look for a .com
On the Support form it says they must have a .com blog - some miss that. (Some even get a blog here then insist on support for their blog elsewhere).
I think the only answer is to accept these posts will always happen.
Make a polite post pointing them to the .org forums. If you see such a post, copy your reply - and then no-one at all reply. They don't need telling 4 times and we don't need that thread being bumped constantly. Just one reply and it doesn't matter who writes it.
And to get some sort of scale, someone count the posts (not the replies) that are mistakenly placed here and are directly related to .org - I doubt there are that many.