Because in the year 2009, a whole bunch of spambots flooded the site with ads for xanax, gucci bags and porn.
As a result, all new accounts have to be approved manually for their first post.
The spam problem continues to this day, I had to remove over 100 spam accounts and they're still coming. They're getting smarter too, and making "human-like" posts on random dead threads but advertising random crap like online casinos and lingerie.
If people could post immediately, then this site would be infested with posts like this:
The LA mod is still available here:
https://www.emergency-planet.com/files/file/337-los-angeles-mod-21/