>>45905202They axed in in gen 6 when fairy type became a thing.
My guess is it was only ever a thing to serve as padding, computers rely on binary so the most optimal numbers to work with are powers of 2, back in gen 1 we had 15 types so there would be one bit unused in the 2 bytes dedicated to bitflags for typing. I've never personally looked at the gen 1 code but from what I've seen in pkhex and this chart here it looks like each pokemon would have stored its types that way and the game would just check to see which bits were turned on to determine the pokemon's type combination, this would also allow for weird instances of glitches where too many or no flags were on causing the game to pull a value for the type(s) that was never meant to be encountered in the final game like missingno's bird type if they were left in the look-up table since theoretically using 2 bytes a single pokemon could have 16 types or certain combinations of 3 or more flags being turned on could have at some point been used to represent more types that got scrapped at some point.
