Long story short, this is a mix of an SE 1.0 third party community called Social Sound Design and the audio related questions from Audio/Video Production. While Audio/Video production ran under the kind of style most people on Stack Exchange are used to, Social Sound Design was a COMPLETELY different site. It had a completely different set of rules, a completely different idea of scope and really ran much more like a question focused forum than a typical SE site.
When SE stopped supporting the SE 1.0 sites, they rolled SSD and the audio side of AVP together to form Sound Design. The historical question base was briefly looked through to do some amount of historical locking on many of the most "non-QA" style posts, but there was a massive trove and only a couple of people to go through them. It wasn't really deemed to be that big of a deal at the time and when a post that didn't get caught in the initial sweep comes up, it is normally flagged for historical locking pretty quickly, but there are still a lot of them hanging out there in the distant past that haven't been worth digging through.
If you have an interest in digging through them, by all means feel free to flag them or get the rep to be able to take actions in the queue directly. I do think it would be nice to clean them up a bit more, but at the moment we don't have anyone who feels that the best use of their time would be in cleaning up legacy posts that were valid at the time they were written and just aren't the way we do things anymore.