I actually have wondered for a long time why MTF would get in trouble, since it's literally the only forum I know where it isn't allowed. For example, at TW it's allowed as well while they have a lot more commercial interests to protect than MTF.
It's allowed at TW? Surprising.. Though I've always found things a little robotic while lurking over there.
Dunno man. I've figured it's something that's followed on from when MTF was joined with TF.