The thread containing the mentioned post has been viewed 1540 times since its opening. icopress's post was seen much fewer times. So the news went almost unnoticed by a large number of members.
The information was transferred to the altcoinstalks forum in a thread that has been viewed 3300 times so far. Also, a very small number of different people saw such info.
Even with research, it is quite possible that he would not have come across this discussion.
I see this problem of lack of information partly in theymos' decision to ban mixers and open discussions about them. Without the mixer ban on Bitcointalk, I'm sure everyone would have been warned much earlier in a much more transparent way.
In the bold part, I am with you. the ban for mixers [and funny enough that mixers are not completely banned, Jambler is all around the forum.] caused lack of information on Bitcontalk. If the mixer operations were normal like it used to be then we would know about it the moment it was happening. Many topics would be created even on their ann thread there would be a lot of discussion to aware everyone.
Altcoinstalks is still not mature as a forum and not many people even know about that forum. In search engine the forum posts are not ranked as they get rank on bitcointalk.