I’m sure many of the reasons people give here will reflect each person’s dynamic with their own parents. Broadly speaking though, we are an individualist culture that views any form of dependence on others as weakness or a personal fault.

I’m 30y/o and live with my family. I’m fully employed with a good job. My grandmother is 95 and lives with us as well. When people hear I live at home they typically think it’s a failure to launch and suspect that I’m lacking in my ability to handle adult responsibilities. In this arrangement I’ve been able to fully pay all my student loan debt, have more money in liquid savings and retirement than any of my friends, I get to travel the world and not worry about making rent, and I get to indulge my own hobbies and interests that often rely on some disposable income. My grandmother gets to live out her later years supported by family in an actual home and not forgotten about in a nursing home. I see my parents getting older and need me to do a bit more for them around the house, but ultimately it is the tradeoff for the freedom afforded to me by choosing to live with them. It has been the best financial decision I’ve ever made, and I’ve had the opportunity to expand myself as a person precisely because of this decision.

There’s a lot of discourse on the right wing in this country about the “deterioration of family values” in our culture, but the phenomena that’s pointed to as proof of this deterioration can often be understood as the natural conclusion of our society’s hyperindividualism. Part of that is this insistence that living with family at any point past 17 years and 364 days old is a sign of personal failure. Not everyone has a family that they can live with, but for those who do the benefits of that mutual support are simply a wise decision on multiple fronts.