The forum is open to the public, and anyone can post anything they want, as long as it's not illegal. Then moderation only has to limit published information that is illegal. Mixers are not illegal, so anyone can post information about them.
So the option of not advertising services that are more sensitive to having problems, is better than having these inconveniences.
That's correct, though; the forum is open to the public just like every other social media platform where, by right, other general members or users can advertise what they like as not as it's not illegal and NSFW.
So with these, mixers signatures don't get banned in the forum, but if Theymos gets a bit tense, he may be forced to stop it. Like I know, everyone has their own motivation for joining this forum. Who knows if these investigation agencies are even among us, hiding and digging up information here every day to see if they can get any valid evidence to used against the forum. As far as I know, this is the only Bitcoin community that is very strong and steadily clean, to aavoid scams and shite stuffs here.