Why don't chickens fly in the sky despite having wings?

The bones of the bird's body are quite hollow and filled with air. Using this quality, they can fly in the sky. There are some basic differences between birds that cannot fly and those that can. For example, the wing bones of birds that are unable to fly are relatively small, their bones and muscles are heavy. So they can't fly. However, forest roosters can fly and sit on high branches of trees.