And even if they don't love it they use it because they get subjective value out of that usage as these people have lots of contacts (or maybe groups) there.

I don't use FB anymore. For more than two years now. But I still keep the account as I have exactly one use case (just anecdata):

There are some very good groups on Facebook for genealogy. Here I can get help when I get stuck again.

So if I continue again with the genealogy efforts I will certainly post there again from time to time.

There are few to no comparable places on the net where I could find the appropriate help.