Probably because vulnerability research is binary - you either have an exploitable bug out not. The fact that people write in depth about things they've found means a culture of openness, IMO.

This is true if you're not really known. (Un)fortunately you need a reputation: need to be able to walk the walk if you can talk the talk.

Once you get over that hurdle, collaborating on targets is pretty common. Made $10k USD last month collaborating with someone in another country, in fact.