Of course, most people want to be in the big cities because that's where the money and good jobs are.
Incidentally, this is the largest and most successful anti-poverty program ever implemented. People whose families have lived in terrible generational poverty, in the same village for thousands of years, in some cases since before the invention of writing, are now able to buy iPhones.
Sure you skip invasive ads and pollution. But your diet is still abysmal, just try living on rice and soy beans for a few months. The healthcare is poorly accessible, while party control, spying, draft etc are just as omnipresent as everywhere throughout China.
Despite what you see as the drawbacks of modern life, the people who have moved to the cities are far, far better off, and freer, than before.