It's not the only thing that exists, but it is still one of the most reliable social media to find someone on, especially for millenial aged people and older.

The group and event functionality is still leagues better than anything else I've seen, so neighborhood groups, school groups, and some classroom groups still rely upon it. For neighborhoods especially, there's no way in hell you're going to convince the overehelming majority of the neighborhood into Discord, Slack, Telegram, or especially any sort of self hosted or federated options while also giving up functionality and convenience.

Let me be clear, Zuckerberg is the strongest argument for the lizard people conspiracy I've ever seen. I am certain thatbFacebook and the horrendous effects it has had on society will be studied for history books for a very long time. It needs to die.

That said, the issue is only so simple as "why do they keep using it, are they stupid?" if you haven't been paying attention for the last 20 years. They've worked very hard to be just barely useful enough, bring enough separate functionality under one roof, and to be psychologically addicting enough to keep people on it.