Freenet was also slightly slower than molasses in Antarctica. You had to really want to post there. The product of a messageboard is roughly:

sum[user_i in users](opinion(user_i)•engagement(user_i))

It's the second factor that causes all of the problems. But much like fast-food companies get a large fraction of their revenue from a small fraction of their customers, social media companies have trouble disempowering highly engaged users when functioning as a profit-oriented business.

It's interesting to consider what would happen with a "less moderated" messageboard where an individual's daily engagement is capped (supposing you solve the multiple account problem). It doesn't seem likely that we'll see that any time soon, though.