Does it make sense at all?
I can think of several factors that influenced Game Freak's decision to make Bite and Crunch dark type moves.
It's important to note Game Freak's questionable decision making for certain parts of the Pokémon games. They don't always make things accurate, such as Cincinno having higher base attack than Hawlucha, who is described by the Pokedex as the wrestling Pokémon.