Given the ludicrousness of the tech interview process, if I have to wait for the offer to ask about company culture, that's too late. I've already put in a dozen hours on the rest of the steps, and passed countless gates, only to now find out I don't actually want to work there with the offer in hand? These things need to be cleared up in the phone screening and the first interview, before both sides have put a tremendous amount of time and effort in.