I seem to recall that threads were never deleted, just closed and locked, so as to preserve the history of the board, with the exception of bot spamming posts being deleted. Seems like lately there have been threads that get deleted due to some form of moderating, even after several posts have been made, and they no longer exists anymore.
Did something change in how issues like this are moderated or has it always been this way and I have been blissfully ignorant?