Your comments

On top of it being a legal grey area (or simply illegal in areas), FA previously suffered legal action due to it, and it's not worth keeping the risk of legal action for cub content. On top of that, personally, it's a matter of comfort- looking around on sites like twitter and other sites it's not hard ot find artists unwilling to set up on FN due to the tolerence of cub content.
There's also the whole argument Deishido brought up which I heavily agree with, and should be good enough reason on it's own.