If Apple were to include an ad blocker by default in Safari it would be the greatest thing they've done for users in the past 5 years. Their privacy/anti-tracking stuff is good but it's largely invisible to the end user. People would never want to go back to the raw internet once they experience it without ads.

Yeah. And, “privacy” is part of their pitch (it’s just a sales pitch, not a moral philosophy, and I’m aware that they don’t always live up to it). Including a default-on ad blocker would be an extremely user-visible way of emphasizing that pitch.