pretty sure it's because they're all mentally ill, delusional, narcissistic egomaniacs with technology addictions and nothing meaningful to live for besides Y Combinator
Up until the final clause of that sentence I didn't have a problem with it (well as a blanket statement it is pretty snarky but a touch of monomania combined with massive self belief isn't necessarily a bad thing when running a startup). All of that can work for you in the right environment.
