Why isn't there a light type?
The Dark and Steel types were created for basically two reasons. One was to add more flexibility to the game. The second was to nuke the INSANELY powerful RBY Psychic types. I'm sure some of you remember the first Pokemon Colosseum where it took SIX Pokemon to defeat the insanely powerful Mewtwo. The Steel type and especially the Dark Type were created in order to counter that flaw. That's why Steel has a resistance to Psychic and Dark has an immunity. And note, NEITHER of those two types are good at attacking.
Not only that, but look at the Pokemon that have that typing. The poster children for Dark: Umbreon, Tyranitar, and Houndoom. Umbreon has NO attacks, but incredible defenses. It's also weak against the type that has around TWENTY-TWO attack moves not counting Seismic Toss. Tyranitar is a Pseudo-Legendary, but its Special Attack Power is not phenomenal, and like most Dark-types, it relies mainly on its superior attack power. Absol can attest to this. Anything that isn't Psychic or Ghost will not take all that much damage from a Crunch, even with STAB. And Houndoom (and also Sharpedo), the only Pokemon that CAN do tons of damage with Crunch, has such pathetic defenses that it's TwoHKO'd by almost anything that has attack power.
There won't be a light type until Dark becomes broken, and because Dark is such a sad attacking type, that isn't very likely.
