Speakers at TED are addressing a wide variety of smart and successful people, and therefore must compose their talks to communicate what actually matters outside their own circle, and make it worth that audience's time and $6000 a year to listen.

Yes, they're well-prepared, but they're lowest common denominator. I think I've learned less from TED talks than from any other source by or about the same person. eg, compare Bruce Bueno de Mesquita's TED talk to his interviews by Russ Roberts. I haven't listened to his hour+ talk on Iran, but I think I listened to a talk that contained 20 minutes on Iran that was much better than his 20 minute TED talk.

Maybe they're good if you just want 20 minutes to filter the person for actual learning later.