I'm a member of different forums and NEVER have I've seen threads held up for approval. .usually you can report a thread and mods will remove them and the mods are all volunteers like you said and they have many but some related to a specific sub-forum.
They're choosing to keep the site free from the things Once mentioned above. And the users not having to endure those things.
As a long time user on this site, around before they had to give approval for threads, I saw many times when people joined the site to provoke and create chaos. People dropping expletives like crazy, verbally assaulting people left and right, posting inappropriate images or links, posting ads for other religions, etc..
Mind you there Are people that can be as young as 13 that join this site. So it's not just about protecting the adults, but the younger people as well.
As for mods, first you need someone comfortable with computers that can utilize the software to do a variety of things. Another important thing is finding people who keep calm when things get heated. And also don't have bias when moderating. There are lots of fiery topics and you don't want mods taking sides or misusing their position against people they disagree with.
I recall a mod that felt free to make personal attacks against people over disagreements. I know first hand. And others I heard from saw the same.
Quite frankly that second part eliminates Many on this site.
People also need to be here long enough to have built a trustworthy foundation and shown they can be trusted.
Eliminate all those people and it really narrows down the list. Then add people who ask to be mods, that's an automatic no. Or people who simply don't want to, even if offered.
Also if someone gets even a few hours to run wild on this site, when mods do show up to deal with it it's not one poster alone. They have to also go through people's reactions and responses and decide if any need to be removed. Or in some cases I've seen hours worth of posts deleted because it was too much to just clean up the problem parts.
Maybe other sites aren't as concerned about keeping trolls and others out. Which may speed things up, but, at least for here, it deteriorates the quality of the site.
And I have seen new users quit the site because someone was running wild and they didn't know if it was acceptable or not, especially if it went on for a while.
I agree with you it would be nice to not have to have new threads approved, but as someone that was around before that, I'm glad they do it this way now.