The thread was either pointless, answered (If you asked a question) or you broke some rule making the thread. They usually give reasons as to why they lock threads.
Check out the Pokebeach Hierarchy thread. Basically Water Pokemon Master created the site so he has ultimate authority, then he chooses people to moderate the site.
Okay, the question has been answered. >_>; Threads can be locked for many reasons. Reasons include anything that breaks the rules, such as thread revival, being a spammy/discussion-lacking topic, or if a thread becomes grounds of a flame/troll/spam fest.
I'll lock this thread since it seems to be generating spam. (Plus, it doesn't belong in this section of the forums. Next time use "Website Feedback", or simply PM a moderator.)
Just to give a last reply, you can always PM the Mod who locked the thread and they can provide further explanation why the locked it. Just a tip so you don't have to make a whole thread on it.