> I still don't know how they're valued at $5B+ when I don't know a single developer who actually uses it anymore

I think most people here on HN is within or close by the "Innovators" part of the "Technology adoption life cycle" (https://en.wikipedia.org/wiki/Technology_adoption_life_cycle). When Postman hit mainstream, it was already bloated and ruined, and "Innovators" had already moved on to something else, but for Postman that's just the beginning, as they're in the "Early Majority" part, and still have a tail to ride, so investors and everyone else can extract all the value from the remaining s̶u̶c̶k̶e̶r̶s̶ users.