People typically move further out so they can afford something larger when they get kids. Since the city is dense you don't have to move very far for prices to drop steeply, unlike sparser cities, so you can still keep your job with a reasonable commute.
I know a lot of people who lived near the center when they were single so they were close to everything, and then moved 15 minutes out when they get kids. Selling those small central apartments give a big boost towards getting a nice home outside the center. Not Paris but the same European layout with dense suburbs, it really isn't that expensive since those dense suburbs are still very close to the city center relative to American sprawl like in silicon valley where you have to drive for an hour to reach a cheap place, in Europe if you drive for an hour you get to the next city so even the cheapest suburbs are much closer than that.
I know a lot of people who lived near the center when they were single so they were close to everything, and then moved 15 minutes out when they get kids. Selling those small central apartments give a big boost towards getting a nice home outside the center. Not Paris but the same European layout with dense suburbs, it really isn't that expensive since those dense suburbs are still very close to the city center relative to American sprawl like in silicon valley where you have to drive for an hour to reach a cheap place, in Europe if you drive for an hour you get to the next city so even the cheapest suburbs are much closer than that.