NSFW ads are never 100% reliably detected or voluntarily flagged, and it only takes one screnshot of Wholesome Brand™ next to someone's penis for it to be a PR issue.
Free hosting for the masses of porn on the internet is a low interest rate phenomenon.
turn them off on NSFW posts?
Tumblr tried that. No NSFW voluntary tagging nor automated detection is ever perfect, so many advertisers treat it as all-or-nothing.