Here's why:
* Dragonair is only found in the wild at levels 38-42. You won't encounter a Dragonair at level 54 in the game.
* Wild Pokemon levels in SoulSilver are capped at 45. Even if a Dragonair were to be found at a higher level, the game mechanics prevent it from exceeding that limit.
If you want to get a Dragonair in SoulSilver, you'll need to:
* Find a Dratini in the wild: They are found primarily in the Lake of Rage and the Dragon's Den.
* Train your Dratini: Level it up until it evolves into a Dragonair.
Let me know if you have any other questions about Pokemon SoulSilver!