The old school BBs didn't have a steady stream of internet riff-raff wandering through and defecating on the lawn. Every single "everything" platform that has user comments has this problem. Reddit and Twitter both make this problem particularly insidious by facilitating cross communication (cross posts and retweets) between the sub groups. It is impossible for subject or niche specific communities to have a high quality existence in this environment. For all their ills at least the chans make a good faith attempt to run "containment boards" to mitigate this problem on their own site.