I agree with you in that I think it
should be like that, but you have to appreciate that not everyone is like us, and not everyone loves in the same way.
Actually, I say I agree, but... I don't know about you, but I spent many years believing my parent's love was conditional. Even now I think it's more of a tolerance. I looked to relationships to give me the love I desired (which wasn't healthy), and I was willing to give up my family and city if necessary. I had a partner in Canada who I loved, and when I went there I saw how beautiful the country is. Growing up I'd hated my town and wished for somewhere more beautiful and remote, but I'd never imagined that kind of environment. So, even though I knew how difficult immigration is, I wanted to move there. It was more difficult for me to picture leaving my best friends than my family. And then my niece started talking more, coming here more often, expressing her feelings (which we didn't force her to do), and I realised that for the first time in years (since my Gran died) there was someone who, for the time being, not only cared for me un-conditionally, but looked up to me; felt protected by me, and the worst things about me didn't matter when I was with her. And I no longer wanted to go, in spite of how much I loved my partner of the time (at least not until my niece was older and more of a pain

). I can't say it ("the worst things about me" not mattering) has been true of any of the romantic relationships I've been in, but I'm guessing this is the kind of family love people have when they find it difficult to choose between their family and their relationship.
Of course, that's not always the case to result in such a situation. For the people who are too afraid to "come out" to their family, maybe
they love their family that way without thinking it's returned. It's all about fear. Some people are too afraid to risk losing or hurting the people who have been there all of their life. We know the latter can be true, because we know there are closet LGBT people who suffer miserably for the "sake" of their families. I think people are terrified of romantic love. Even when it consumes you, you don't necessarily believe it'll work out. People want something to fall back on.
So, although I agree that we do need to build our own lives as adults, we have to appreciate that not everyone does this (or will at least take longer to do it), even if you think it's silly.
A balance would be ideal. Everything out in the open and everyone getting along, ha. A lot of relationships where one person is in one situation (loving and accepting family) and the other's circumstances are different (won't come out to family due to fear) won't work out in the long-run, especially when it's a young couple.