People seem to think that all Backpage did was run ads.
That's wrong. You should read what they actually did.
https://www.hsgac.senate.gov/imo/media/doc/Backpage%20Report...
You should read what Backpage themselves were saying. They claimed that the Communications Decency Act means they had no responsibility for that ads that appear. This was tested several times in court, and the courts often agreed with Backpage.
So, after those court cases Backpage knew that ads were appearing because that was a finding of the court.
Please read pages 7 and 8 which give details of some of the cases against Backpage.
EG
> Although the court concluded that the plaintiffs “ha[d] made a persuasive case” that “Backpage has tailored its website to make sex trafficking easier,” it nevertheless upheld the dismissal of the suit under Section 230 on the ground that the site’s features did not render Backpage a content-creator. The court noted that “[i]f the evils that the appellants have identified are deemed to outweigh the First Amendment values that drive the CDA, the remedy is through legislation, not through litigation