What warrants a thread being deleted?

I swear the criteria for deleting threads make no sense. I make a thread asking about the dumbest PED accusations people have heard, it gets deleted. Yet we can have people throwing in genuine accusations against boxers which feature occasional flaming and racism. I even once made a thread asking what danny garcia and Broner can do to regain respect from fans and that got deleted too. Yet here we have threads with guys offending each other based on religious beliefs or people insulting eacjother for being fans. Where's the logic in this? I'd like to know why some harmless threads I make which provoked civilised discussion are getting banned while threads filled with racism, PED accusations and flaming as a whole are still on nsb to this day?