Most people live where they are many jobs. Most people live close to their parents. They were able to find a job close and so choose that. Generally if you look for a job you can find plenty of them in whatever field you are in.
Now jobs are the most common reason to move away. However that is still a minority situation, the majority find a place to live and then a job there. Even when looking for a new job people tend to prefer jobs where they don't have to move.
Depends where you live. In the US people move for jobs a lot, we studied that aspect of US life in French schools. In France it's common to move to Paris to work once you finish school.
The advantage in France is that friend cohorts are likely moving to Paris roughly at the same time. But moving further out into the suburbs or returning to the province / a city nearer their hometowns to start a family is comparable to the US - just my guesstimate.
And as someone else pointed, friends living on the RER or opposite side of Paris might as well live in another city, unless meeting up somewhere halfway instead of at someone's place, but that can quickly get expensive.
Now jobs are the most common reason to move away. However that is still a minority situation, the majority find a place to live and then a job there. Even when looking for a new job people tend to prefer jobs where they don't have to move.