I've seen this explanation coming up quite often in discussions around Qualcomm or other similarly sized players: you have to be ordering (very) large numbers to be able to get their attention. Documentation is provided under NDAs I hear, and if you'd let's say, decide to buy a small(er) number of boards off the grey market (from one of their direct customers), you'd still have the problem of lack of support (firmware/code, docs, etc).