While the conversation is taking place about whether the forum could have possibly been seized after
Sinbad was seized, there is a valid question that remains unanswered: If the fear was that advertising mixers or allowing them to operate signature campaigns could lead to the forum being seized, why was the Altoinstalks forum not seized even though promoted mixers throughout?
Altcointalks is incomparable to Bitcointalk, though, especially in terms of activity or site visitors. Those law enforcement agencies obviously first go for the most popular platforms. Which is why they would go for the likes of Chipmixer and leave out the smaller Bitcoin Mixers
Until recently, they were in the EU, but a few months ago the site was moved to servers outside the EU to avoid possible complications with the MiCA regulation. The owner is also not from the US, strange but it is possible that there are non-US sites.
Domain seizure can happen to any platform regardless of the jurisdictions they are operating in.