All the "I don't have Facebook" talk is proof why forums fail.
Just as a disclaimer before someone jumps in; as a private person I can say that I have never ever been registered on Facebook. I doubt all the "I don't have Facebook" users can say that, because I believe at one point they were registered in the last 10 years or so. But ditched it later. Not in my case. I never "tasted the honey" so to speak. So, if one wants to brag about it, I can do that, too, and more than most people.
Now, let's get to the point.
If you want to be a hunter, you must go after your prey.
And if your prey (your target audience) sits on Facebook, you bite a sour apple and follow them. You must present yourself "in the community" so to speak. Be a member of their Facebook groups and if the occasion presents itself, forward people to your site for "more".
And now my site has its own Facebook account and I participate sometimes in several groups and have a lot of private talk.
Like it or not, especially all the old farts who generally are non-tech-savvy, they do sit on Facebook. You need to be seen by them, they won't come to you, you go to them. They barely know how to navigate through the internet, so normally it would be a surprise to find them on your forum. Hence why you make yourself seen by them.
Whatever you call it "play their game", "play the game by their rules", "following mainstream"... "wherever the stream shifts to", you must be there.
You can't close your eyes and watch the ships sail away. You must follow them.
Same can be said for mobile phones. It gets more and more important. Closing your eyes will fail, thus why forums fail.