I am on four forums: this one, one for my profession, an RV one, and one for my truck. I haven't posted, regularly, on two of those forums, for years, and only joined the truck one in the last month, to work on issues with my vehicle.
I think people on many forums, at once, can't help but be spread too thin. I view them in the same way I've viewed old acquaintances whom I used to see in various social gatherings, working the crowd: Insincere people who care that you listen to them, but don't actually give a damn about what you're saying to them.
My step sister, from my dad's second marriage, was astounding, that way: You could be talking to her about an important (to you) subject, and she'd pick up with an entirely different subject, about herself, once you completed your sentence.
I only knew one other person, a macrame artist, who approached being as horrid. Talking to her felt like you'd entered The Twilight Zone because not a single conversation made any sense, for being entirely disjointed.