#he basically

Me: Why? Do you miss him, darling?

Odo, later: If I did have a brother, even as worthless as Quark, I wouldn't let anyone come between us!

"Honestly? Those Pokémon who can fly are the most difficult ones to tame, besides dragons.

Think about it... Humans can do whatever they want as long as they're standing up somewhere. This gives them more power than they should have on the ground. Destroying forests, building cities wherever they want, making science evolve to have more of that power... They can use all that to try to be superior to Pokémon. That's why those Pokémon who live in solid land are the most vulnerables to the harm humans cause.

Water-types should be safe, but of course, it isn't like that. Water can be easily wasted and damaged. Humans pollute it non-stop, which causes the death of many Pokémon who live in the sea or in rivers.

Thus, the sky is the best place for a Pokémon to live in our current world. It's the safest, far more than land and ocean are. It shouldn't be like this, the three of them should be safe, but it isn't. That's why Pokémon on the sky are usually the most difficult to catch. Humans can't build anything on the sky. They can't live in the sky permanently, even if they can fly in planes or with Pokémon's help itself. They can pollute it, yes, of course; but it's not as damaging as water pollution.