It seems like it's been that way since Generation I.
I don't really mind the lack of Fire-types; that's one less in-game type to threaten my dear Snorunt and Seedot [after I finish my Snorunt project].
Snorunt project? Why would you mention it if your not gonna share with the class? lol
Fire is too one sided imo, hence why there are more water types, ANY fire type is godly. So they need to weaken it via water type. Specially since Japan is surrounded by water, they notice fish and such easier. Thusly comes to mind faster when making new poke.
Don't forget you can now find Geodudes in grass XD