On the other hand, administrating even a moderately sized forum (or a mailing list) was a shitshow in itself. You'd deal with constant attempts of people trying to 0wn your server, to DDoS it, or to spam - and phpBB being a constant exploit source didn't help either. And then on top of that you'd have to deal with people attempting to use your server for illicit stuff - CSAM, warez, porn, you name it someone tried to abuse your system to spread it. And on top of that you'd have normal moderation duties: trolls, hate speech, flame wars.

And if you'd get really unlucky, the pigs or MAFIAA would come sending nasty C&D letters, subpoenas or a court-issued search order for some shit some of your users did.

So many communities switched over to Reddit simply because Reddit would take care of anything but "normal" moderation duties.