Surely the single biggest reason is posting photos. Since photobucket tried to screw every forum/poster, people probably thought sod losing everything they’d spent so much time documenting, whereas on fb, photo hosting is a doddle.
I went and got my own domain with hosting for pics, but everything has moved to fb groups it seems. Pity, I far prefer forums. Now I just document everything I do on my own private blog, at least I have a record that won’t get sabotaged by a free/greedy photo hoster or a forum that doesn’t pay their bill and goes tits up or whatever. If forums had easy and free photo hosting they’d probably still be busy.
Sign of the times, it’s happened on a few forums I’m on that people have migrated to an fb page.
"She'll make .5 past lightspeed"