Why don’t “Western” scientists form scientific communities on Facebook?

Pure speculation here -- I've worked with scientists for a long time, but it's been a while and I no longer know how those circles work.

My guess -- Facebook doesn't bring any value to them. Scientists have had strong and deep international communities and very effective methods of communication within them for generations. Facebook would have to provide some sort of serious advantage over what already exists to lure scientists over to it. I don't see that FB offers any sort of advantage at all to that circle, let alone a serious one.

Because scientists are aware about privacy abuses of Facebook more than any other community

There are a few scientiats and doctors in the carnivore groups on facebook