I am from a generation which grew up with phpBB forums of various kinds, and I loved the format. I still struggle with understanding why we can't remain within decentralised forums. Was it such a hassle to check like four URLs a day to see what was happening in the threads you participated in? Are centralised feeds such a core necessity to us?
Popular forums are high value targets as they both tend to be central in the PageRank graph (so link spam has historically paid off very well as black hat SEO); while also sitting on large user databases with associated emails.
So there are non-stop intrusion attempts and ceaseless bot spam. Operating a forum is a lot of thankless maintenance. It's not made better by the fact that a lot of the older forum software had nightmarish upgrade procedures.