It's been happening for a while now. Slowly, they have stopped posting. (I'm pretty sure we all have some of the same members in mind.)
I know many quit posting in this section (but still post in the show section a bit) because they got fed up for being criticized and accused of being rude every time they tried to answer questions. Often, the best answer to a breeding question that is in the best interest of the dogs and the breed in general is not the one that the askers like hearing. But sadly, instead of appreciating that someone with years of experience took the time to give them a well formed, honest answer, they lash out at those where were trying to help.
Who wants to continue to take time out of their busy days just to get that kind of reaction out of people? You'd have to be crazy to do that!

Fortunately, many of them are still members and still post, just not in this section. (Many still post frequently in the show and other sections.) Most of them will take the time to answer questions via PM and are always willing to help those who really do want help and who are open minded.