It's not hard to to write significantly more robust software than what you get on a late '90s LAMP stack. What killed those forums was the constant upkeep neede

It's not hard to to write significantly more robust software than what you get on a late '90s LAMP stack. What killed those forums was the constant upkeep needed to keep them secure. Most of that is historical baggage though. The software emerged in a time when the threat landscape was completely different, and things like data portability wasn't even a thing. The problem that remains is spam mitigation. Bots are very hard to detect, and there really aren't any good distributed approaches afaik.