Reading the article, it appears that Zuckerberg is trying to get his staff back operating like they are a startup with events like a hackathon. That his staff are no longer participating is indicating that they aren't treating Meta like a startup any more.

It isn't that Zuckerberg wants his staff to act like they are having fun, but to get back into a startup mentality where they will hopefully over perform and are instead treating it as a job where there isn't an incentive to work harder.