Honestly the fbi just isn't as zealous as you want them to be, they are looking for traffickers, actual sex slaves, producers of CP and more significant distributors, if something might pass dost they ignore it and as for distributors of CP there is genuinely a big fbi file hooked to an image analyzing algorithm that they have installed on most sites with over 10k users that checks all images against a local but encrypted cache of known CP. If an 8mage earned a conviction they are more likely to jump at a prosecution. However they are far more interested in never before seen or unreleased CP and even then distributors and viewers are way down their list compared to traffickers and actual producers of CP. Most of the FBI's budget is spent on stupid shit like watching us. Anyway they treat CP like piracy, they go after the distributors that are easy to catch first and often ignore the people searching it out for a few reasons, firstly if you scroll by the errant CP post on 4chan you technically have CP downloaded to your computer, same if you searched it out but never actively clicked "save as" on an image or video, the fbi might win in court on such a case but they could lose because you can claim unintentional possession and if they did lose then the ability to intimidate these people into a quick plea deal is lost forever. As for big tech like I said above leaving up these kiddy porn pages is essentially a honeypot the fbi will fall back on when big fish arent getting caught in the typical nets.