"The smartest people" were not working on ads because building an advertising behemoth is not a smart thing to do.

When there's nothing good being invested in, "the smartest people" are simply underutilized. They do things that they think are good instead.

"The smartest people" have never sought maximum capital accumulation, and have not historically been driven by "highest wages" jobs.

The computer industry formed out of WW2 because a bunch of smart people ran into each other and did what they thought was really cool and had realized was suddenly possible. Von Neuman literally met one of the other guys and discussed computers as a theory at a train station and that meeting was influential on the future industry. They did not try to make billions of dollars. They had fairly average jobs that paid average. Often working for the government itself.

"The smartest people" did not work on targeting ads at people, and while some of them may have been involved with early transformer work, they certainly would be disillusioned with LLMs by now and would not be working at companies burning trillions on them.