Why is pulmonary respiration on land more promising than branchial respiration?

On land, most representatives of the animal world carry out gas exchange using a special respiratory organ. They are lungs. They absorb and release air. The gills are needed to obtain oxygen not from air, but from water. If animals that live on land had gills, then they would be dependent on the constant availability of water. They did not spread far from water bodies. But there are some exceptions. Some inhabitants of the aquatic environment do not have gills, but lungs and vice versa.