Have to agree the social media sites did hurt the forums. But I think that the use of the internet is changing, being a mod on a number of forums, I see the number of one and done members increasing. Were they ask a question get answer and don't even bother to acknowledge the answer. And the ones that don't want to waste their time googling.
I had a women tell me her time was to valuable to waste googling for the answer to her artwork question. And she got mad when nobody would answer her other questions!
The stak is still going strong, only because of the wide subject matter it covers, Harry has classifieds, and the show forums for non profit groups. Plus it is about the only game in town for full size steamers.
I was a mod on a metal artist forum that was at one time the best on the net. And it is going down hill. Owner has other interests, and life is probably getting in the way. So when he wouldn't answer some problems, I tried to get him to take me off as mod, he still hasn't after about 4 months.
The social aspects of the other media sites brings a wide circle of people together. As most don't want to join a group if they don't have an interest other than friendship with a member.