>>7,11More probably, they didn't like retaining terabytes of data for a dwindling number of users. Remember, Usenet was mostly dropped by 2005, when storage was a premium, and most of the customers were content have fetish cybersex on Yahoo groups.
And now for a story about CP on Usenet:
I know of only one group that operated on Usenet, using completely encrypted messages in an abandoned newsgroup they had appropriated. Predictably, it took real police work (if I recall correctly, according to the affidavit, the fat guy had a painting in the background of one of the videos that was only printed in a run of a few thousand or something as part of an art club thing, then a bottle of water that was only distributed in the southern US, and the interior of a car. They got the records for the art and pulled up vehicle registration records to narrow it down to a few men and cracked the case) to find one member and get him to rat out the others (pedos aren't known for their solidarity), which is a Good Thing, because the FBI says they were into some seriously shady shit. There are most probably others of course though.