To take it in the other direction, maybe Earth has retained the large-scale heavy industry that a society of bubble cities wouldn't have the room or materials for: Venus retains some nanotech and biotech, Earth has become a Rocketpunk world with huge booster rockets launching atomic spaceships. Mighty reactors power factories of metal and concrete, where advanced mass production fills the sky with flying cars and homes with robot maids.
STARGAZING: All I see are the lights of a billion places I'll never go. --Howard Tayler, Schlock Mercenary
"It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change." Charles Darwin
"It is the duty of the writers to seduce me into suspending my disbelief!" Paul Beardsley