If they want children, they’ll need more room. Same if you want/need a home office or to move an elderly parent in. I wouldn’t really classify those things as “feeling nice”, more going through natural life stages that renting a 2 bd may retard.

We have kids, we're a bit crammed in our current place and we're building a 3x bigger and much nicer place. Location is a small LCOL country in Europe with high foreign income. So, I see your point about naturally needing more room with kids, but there is also a lifestyle upgrade factor for us. We would be comfortable with 2x the space and without modern / luxury finish, spending less than half.

The rent I pay now is 1/12 of the rent I would get charged on the property I'm building. I'm happy paying my current rent, but I would never rent a fancy property and spend all that money with no equity, even if it would be less than 30% of my monthly income.