People typically max out their housing budgets on urban apartments for themselves/their partners, but want kids to have their own rooms. To get the additional bedroom(s) for no more money, you have to compromise on something else, like location.
Also, suburban housing has the price of a decent school district built in, while in the city you need to pay private tuition for access to an institution which isn't completely non-functional (i.e. overwhelming majority of students are far below the extremely unambitious academic standards).
If urban schools were high quality and middle class families could afford family-sized apartments, things would be different.
It sounds like a lot of the issues here are very different depending on the country you live in.
Edit: No need to be so cryptic, right? Urban public schools are the top tier in my country. Affordability of housing in city centres is becoming more of an issue, but given the availability of jobs, I don't think it's a major driver of relocation.
In general, the situation here seems to be that a lot of families would prefer to live in a less urban environment, but cities make more economic sense still.
Also, suburban housing has the price of a decent school district built in, while in the city you need to pay private tuition for access to an institution which isn't completely non-functional (i.e. overwhelming majority of students are far below the extremely unambitious academic standards).
If urban schools were high quality and middle class families could afford family-sized apartments, things would be different.