Living with parents/in-laws after marriage. How do you justify it?

I'm from a tier one Indian city, my parents are in their late 50s. I grew up in a nuclear family, so I absolutely cannot relate. I also moved out of my parents place very early on since I went to college abroad, worked abroad for a couple of years. As an adult I've only lived the pandemic years in my own parents house. (just some context) But how do people choose to live with their parents or in-laws after having a spouse in the picture? If my grandparents ever moved in with my parents I'm 100% certain my parents would get a divorce. Everyone is very very protection of having their personal space and this trait applies to my extended family as well. I know only one aunt of mine who lived with her in-laws. In-laws died a while back, but for a major part of her life they were present. My dad's only sibling and his ex-wife + cousin also never lived with our grandparents.