In a very interesting essay on why birds won't drive bentleys, Antone Martinho-Truswell explains that the ability of birds to fly is a hindrance to their evolution into complex cultural organisms like us, in spite of having big brains and long lives, the key ingredients.
Flight is a very rare feat in biology. Only insects birds and bats have achieved it. Flying enables birds to escape predators and calamities easily, and go to great heights and distances in search of food.
That way flight is a big convenience for birds. It is a strong survival resource and makes them very fit in the evolutionary sense of the word. There is no pressure to evolve other traits when the avians are so well off flying. A crane may just fly off to a cooler place when one place gets heated up. It doesn't need to worry about environmental conservation even though it might have competent brains.
As the writer explains, the ability of flight is like a black hole that won't let the birds escape and develop other traits.