Because Dragon types are only hurt by Ice type moves and other Dragon type moves. If only Ice type moves hurt them, they would be too strong. In Pokemon X & Y, the new Fairy type also hurts them due to Dragon types being too over-used in the meta game and competitive battling.
The moves that are super-effective against Dragon types are:
DragonBreath, Outrage, Twister (Generation II), Dragon Claw (Generation III), Draco Meteor, Dragon Pulse, Dragon Rush, Roar of Time, Special Rend(Generation IV), Dragon Tail, and Dual Chop (Generation V). Only the first four moves are fairly common, so Ice type moves are still the most vulnerable to Dragon type Pokemon.
There were no Dragon moves in Generation I (Pokemon Red, Blue, and Yellow) besides the fixed-damage, non-super effective Dragon Rage.
all ice moves are super effective against dragon as well as other dragon moves.
Dragon type moves are only super effective against Dragon type Pokemon.
Dragon type moves are not very effective against Steel types. Dragon and Ice type moves are super effective against Dragon types.
Dragon-type moves are super effective against Dragon-type Pokemon.
Dragon type Pokemon are Super effective by Ice types and also Dragon type moves :D
See, electric type moves are effective against water Pokemon. Thunder or Thunderbolt are powerful attacks very effective against water Pokemon such as kingdra. ACTUALLY, since Kingdra is a dragon type too, electric type moves are just normally effective. Dragon type is super effective against Kingdra. But then Kingdra would be supereffective against you too!
Ice, Fairy and Dragon-typed moves are very effective against Dragon.
dragon and ice moves are super effective against garchomp
Dragon moves are only super effective against other Dragon-typed Pokémon.
Ice, Fairy and Dragon-type moves are super-effective against Dragon-typed Pokémon.
to defeat dragon types use fighting type moves. they are super effective.
Depends. Water is not very effective against Dragon types. However it is possible for most water Pokemon to learn ice type moves and these will be super effective. Good luck!