Looking at old defunct forums and blogs on the Wayback Machine, spam and security problems are frequently-cited reasons for shutting down or going read-only.

Over time, the internet has gotten more hostile.

To figure this out, we have to start with 100% and then subtract the chance we're in a Truman Show world run by producers who think math is hilarious. Because nobody thinks math jokes are funny we can subtract zero and be 100% certain.