Why are there no Gen 1 Dark types?

[giradialkia]

Except Togepi's evos had their Normal typing replaced by Fairy despite being dual typed.

Good point, but by comparison the Fairy type was much more.. compatible with designs of the older Pokémon who received it (for the most part). Togepi itself was retyped to pure Fairy type so that changed the whole line from the get-go. And X and Y were 13 years after Gold and Silver, so a change in methods isn't too extraordinary. :P

 

[Tek]

They changed bite to a dark-type move, which a lot of pokemon learn. It sure would have been cool for Arbok to get a dark typing, though.

 

[stp]

Mega Gyarados should have definitely been Dark-type. It's Japanese name, Gyaradosu means "to pierce flesh" or "to stab". If that's not dark for Pokemon I don't know what is.

Mega Gyarados is Dark-type. It's Water / Dark.

I would have liked to see Raticate made Dark. Definitely Arbok too.

 

[Zorogami]

I think the only Gen 1 that would fit the Dark type are the Ghastly line and Arbok really. Since Ghastly - Gengar are already dual typed, i guess they didnt want to change that. Arbok getting dark type would have been pretty cool and made it more relevant...too bad