why don't most of the pokemon with levitate have D-world abilities

Question

E.G. Gengar

Answer 1

According to Bulbapedia : Some Pokémon do not have Hidden Abilities because they are defined by their ability, such as Slaking, Shedinja, Castform, Plusle, Minun, Arceus, and many Pokémon with Levitate; however, some may still be encountered here.

Comments

I already wrote such a similar definition in the question http://pokemondb.net/pokebase/36129/what-pokemon-dont-have-a-dream-world-ability
This question is more specifically focused on the reason why the Pokémon with Levitate have no alternate ability, not alternate abilities in general

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Either way, he answered the question. What's wrong with broadening detail?

Answer 2

Because then they would lose their immunity to ground attacks and area traps and because it's kinda weird that Pokémon with levitate that obviously are not of the flying-type suddenly are not flying anymore.

In my point of view the ability Levitate is something like a third type of a Pokémon, for all flying Pokémon not of the flying type. So, yeah, it would be wierd to have them not be able to fly anymore.

Comments

Who in the world voted this down?