Why is Normal/Flying combination so common?

Birdlike Pokemons like Pidgeot, usually have Normal/Flying types,but why is Normal/Flying combination so common? And why do they have Normal type, instead of just Flying?

Pleaselog inorregisterto add a comment.

They have that type because they can use Roost. Roost takes away the flying side of a flying type. So that’s why Tornadus doesn’t have Roost. Flying types need an another type to use Roost. If Pidgeot uses Roost and it was only just a flying type it’s new type would be ???.The Normal side is to prevent that from happening.So Roost is used Pidgeot heals up. Pidgeot just lost its flying side for that turn.So it would be a Normal type for that turn and it goes back to a normal/flying type at the end of the turn.

This because these Pokemon are based on birds. Take Pidgeot for example it is based on a Pigeon.In real life can Pigeons blast water out there mouth or make thunderbolts?NoPigeons can fly and walk so that is why they are Flying and Normal.Flying= Flying Normal= Walking.

Hope this helps ^.^

This is just my two cents

Maybe they put in the Normal typing to indicate that these birds are actual birds, and to show they are taken from real life, they are given a “Normal” typing, trying to say they aren’t abnormal birds like, say, Zapdos, Articuno and Moltres.

Maybe they wanted to spice it up a bit though it’s unlikely it would be this as then they would have given some other type like…psychic.