Maybe there could/should be a 'broad' SE site alongside every 'normal' one? The 'too broad' questions include most of the interesting ones to read. The ones that are 'intellectually interesting'.[0] It's a shame. I love how you can ask anything on HN without being shut down like that. It's so unfriendly, hurtful even. (At worst on here, no-one answers - no harm done.) Why they can't just let 'too broad' questions go for a day or two to see what responses come in, and delete the page if it sux, I don't know. The mods get points for closing things, I guess. Often they don't understand the question, it seems.
[0] e.g. https://mathoverflow.net/questions/43690/whats-a-mathematici...
Well, bizarrely the close notice on that says "This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet." Which seems absurd. (Although sure, the question doesn't help people, the answers do though.)