IIRC the idea is that (1) it allows third-party cookies of the websites you actually use (like Facebook so FB integration works), and (2) it allows cookies on new websites for the first day or so, and then it starts blocking them.

More info: https://webkit.org/blog/7675/intelligent-tracking-prevention...

But "FB integration" also tracks you?

There's presumably enough users who actually want that behavior from FB, but not from other sites.

Apple left ad blocking to third party developers. You can find plenty of ad blocking apps on the App Store. I imagined they did this for political reasons because they don’t want to the arbitrator of deciding whether something is an ad or not.