>>33315666It matters conceptually, not in gameplay.
Bug types, Dragon types, Rock types, and Steel types usually have that as their primary type, because they LITERALLY ARE those things, so they're 'primarily' those things.
They make them secondary types when appropriate. Like how Dragalge isn't literally a dragon, sea horses are just nicknamed "water dragons" in Asia. Plus they wanted to emphasize how poisonous it is, so Poison is the primary type.
With Hydreigon, it clearly IS a dragon, but that type is secondary because it's just really, really evil. I know I sound like I'm crazy but whoever is in charge of finalizing the pokémon types clearly does so deliberately. You can guess a pokémon's primary type 90% of the time just by looking at it.