As another former Facebook employee, I mostly agree with this. One nitpick is that although you may have not looked at the holdouts often, somebody definitely

As another former Facebook employee, I mostly agree with this. One nitpick is that although you may have not looked at the holdouts often, somebody definitely did. Different teams use their holdouts differently, but leadership probably looked at your holdouts at least a few times per quarter. And now with recent infra and changes, it's very likely that data scientists or product managers somewhere in your org are responsible for explaining results to higher ups at least quarterly. All that is to say, the cause isn't that Facebook (and Netflix) aren't thinking about or monitoring things in the long term. It's that they are measuring the wrong things, because it's very hard to measure things like "this is clickbait".