Why does HN have this "if they won't bet on it, they don't believe it" mindset?

In quite a lot of sectors, gambling on a prediction market for an outcome you can influence is frowned upon, unethical, even illegal.

To be clear, I am talking about the investment analysts who have a role in setting the IPO price, which is a (then-private) decision, not an outcome of a market. It would almost certainly be a crime for the analysts involved in pricing an IPO to make prediction market bets.