IDK, I get it. Grad school sucks. Post-docs suck. Pre-tenure sucks. Post-tenure isn't any better. For that entire period of time you are working on de facto fixed term contracts. Which is extremely uncommon among salaried engineers, and those that take these sorts of contingent employment contracts are typically paid quite well. It's like 10-15 years of low pay, "will I have a job next year?" stress, and moving your family around all the time (or, more commonly, just not starting a family).

And not even for good pay. These days, even after a decade or more of experience, you're making less than your undergrads. Half as much or even less in some cases.

So, your undergrad once-peers start retiring -- or at least thinking about it -- around the time that you're finally transitioning from de facto fixed-term positions to something resembling a normal employment contract, but, again, for a third to a fifth of what you'd be making in industry at that point in your career.

So, yeah, people say fuck it and cash in on influence/engagement/reputation where they can. The only real alternative is the public sector paying researchers better, but that's never going to happen.

While true for many/most PhDs going the academic route, I somehow don't think this held true for Yann LeCun. None of this answers the question of "Why FB?" - he could easily make a slightly smaller boatload of money if he chose to go somewhere else.

Also, TBH I doubt he has much to do with the AI used for engagement optimization, his specialty is in other topics and he seems to be focused on the work of Facebook AI Research (which openly engages with academia and so on). And to be fair he is also still a professor at NYU and has students there.

Same reason why back in the day, a lot of people got electrical engineering degrees but went into software development or finance. The skills were transferable, and the pay was a lot higher.