I don't know but I'll bet Neal has boards for other games because people asked for them...or because he likes them himself. Many people play many types of games, and like finding out which other subsimmers also share their other passions.
It's not like there are specific forums for IL2 or Everquest here; and the 'other' forums are not on the SH3 boards. Maybe the General Topics forum should go, since it's not about subsims. Me, I don't think so.
Like Dowly said, no one forces anyone else to read the other forums.