Why is Family Guy rated TV-14, and not TV-MA (unlike, South Park or Rick & Morty)

Can somebody please help me on this, I mean FG is very gory, and while comedic and animated, it's probably more graphic and frequent then South Park or Rick & Morty, and there's also graphic sexual references and very off-color humor.

(Note: this is not to critize the show, it's one of my favorite cartoons, it's just a question).