Coruscant, which is the city-planet capital of the Star Wars Galactic Empire, supposedly has a population of around three trillion. This is about 430 times Earth’s current population, but even this many people wouldn’t be enough to create a proper city planet here.
To give all of Earth’s landmass the same population density as Tokyo, you would need 895 trillion people, or 300 Coruscants. Even the more pessimistic projections from the United Nations suggest that the Earth’s population will peak at less than 100 billion people by the end of this century. Spread across all the land area on the planet, that would give the world an average population density lower than that of Barnsley, South Yorkshire (pictured) which is hardly a sprawling techno-metropolis.