> It seem more like a stupid decision done by someone that became successful by being in the right place at the right time

This is massively underselling what led to Facebook's success. As someone who started using Facebook-alternatives in 2001, there were a ton of competing social networks at the time. Many very superficially similar to Facebook, and many with a multi-year headstart. FB drove them all to extinction and became the social network via a combination of great product management, and engineering execution. And this was all led by a teenager in his second year of college. The vast majority of people in his shoes would not have achieved the outcome that he did.

I think a combination of the tight control over design/aesthetic (no customization) and the exclusivity was extremely alluring and created the first wave of adoption that just cascaded. I think timing really was a massive deal at that point. Clubhouse attempted to do this recently, and had the same massive wave of initial success, but struggles to maintain that growth because the product itself isn't very interesting.

I think the point is that it is too soon to say the bet hasn't paid off, maybe it pays off many years from now.