It's not a bad thing necessarily but it seldom works well practice. Dating as an adult living with your parents is super awkward. How many women want to spend the night at some guy's house and run into his parents in the hallway the next morning? Ick.

Ambitious, upwardly mobile people often have to move for job opportunities. Meanwhile their parents are often not yet retired and are tied to a different location by their own careers.

The interpersonal dynamics can be really toxic. Often the older generation has particular outdated ideas about household management, religion, cooking, and child rearing. Clear boundaries have to be set and respected or else there is constant conflict and resentment.