Because that is how this world works. You may be new out of the womb intellectually speaking, but if a child shows up at my doorstep one day and tells me I'm on his ancestors land from 300 years prior and I must vacate the home I bought and have legal title too, on the land my ancestors fought and bled over 300 years prior, even if they were assholes about it at the time, I have zero obligation to hand it over because of feelings.

That is why. You may not find it fair, but there does come past a point where the only fair thing to the present society, that had no hand in the original act, is to "keep on trucking" as they say.