I don't think the moderator on duty is just sitting there reading every post that appears on every thread on every topic. For a start, there are a LOT of posts on a LOT of different topics, and the posts keep on coming, so while they were reading one thread, a dozen others could be filling up with new posts that they haven't seen. Try timing yourself to just read every post without even stoppping to take any actions, and see how long it takes.
A couple of days ago, I was sitting at home with nothing else to do, so I reported over 50 spam posts - more were arriving as fast as I reported them, and some appeared more than once because they had had another post added to them!! It would take a moderator the same length of time to do whatever they do with each. This is now not something that can be done manually, the spammers are automated, so to defend against them, the websites have to adapt to match. That means employing programmers to alter the files that deal with posts behind the pages, which can't happen overnight and isn't cheap.