Actually, no. The bloodline is the legacy. At least, that's what most people believe. The accrual of wealth along a bloodline is all about increasing the chances of future success for the bloodline.
Most of the time you hear people talking like what you described, it's within the bounds of and from the perspective of religion. The legacy is new faith believers. You can tell because the children never own their own spirits or selves.
I have a child and I do consider her a legacy. She won't be getting a lot of money. She'll get some. Her quality of life, averaged out, will be less than mine. But so will everyone's; we're in a collapse. Prior to WWII, talk about each successive generation being better off wasn't a thing. It couldn't be guaranteed. My grandparents grew up during the depression, meaning their economic condition was worse than that of their parents (during their childhood). It was post war hubris bolstered by propaganda that started that nonsense talk about bettering each generation.
It was never sustainable and could never be a guarantee.
So that's no reason to not have children and you're not selfish if you can't leave for them what was left for you. Especially, when your economic condition is only partially in your own hands.
I did not choose to have my Urchling in order to have a legacy. I did not think of her as such until she was born. Being one is not because I think I own her in any way, shape, or form. She's her own person. She has the right to refuse the legacy.
Urchling is a legacy because she carries the familial DNA. At this point, she's the terminus of the family line. If it continues, it's through her. She carries cultural memory and learned knowledge that will be needed again soon for those who want to thrive in the coming years. Not many people know how to live off the land. She does. She also seems to have inherited some innate skillsets, like her ability to pack and I don't think she knows how to get lost. Most people can't navigate outside their house anymore without GPS. She's got that natural technical acuity that runs in the family. All the things. Those are legacy too.
I did not have her for that. I had her because I wanted her and I felt like I could do decent by her and raise her up to be strong, independent, and competent. I knew I'd love her like crazy no matter what.
She's not obligated to have children of her own just to extend the bloodline, take care of me in my old age, follow my beliefs, or any of that jazz. I rasied her to be her own person, not a servant. I don't understand people who talk like that any better than you do. There's something wrong with them that they'd think like that.
Legacy is one of those broad words that means different things to different people. To me and many others we are all legacies, for good and for bad, of those who came before us. Their successes and their failures. The things that happened to them and the things they did. We carry their traits; the strengths and the flaws.
All of that is legacy because it is what is left behind when our time on this Earth has concluded.