Here's why:
* Nosepass is a rare Pokémon. It's not found in the wild in any other locations besides its swarming areas.
* Swarming is the only way to encounter Nosepass. When a Pokémon is swarming, its encounter rate is significantly increased, making it possible to find it.
* Outside of swarms, Nosepass only appears in specific locations. These are usually limited to events or special circumstances.
So, if Nosepass isn't swarming in your game, you won't be able to catch it in the wild.