If my knowledge of subreddit drama is correct, diyaudio was around first and after it grew a community, the original moderator abandoned it. Not only did he abandon it, but he refused to let new mods in to run it. So it became a less than stellar sub.
Some folks who wanted to improve the dead diyaudio sub banded together and made diysound which had real moderation and wasn't simply neglected. This sub grew while diyaudio was decaying away.
Given that diyaudio is up and running again, I guess the original creator either finally left it to new moderators, or he decided to get active in the community again.