2. common sense. Nomadic tribes are nomadic for survival. How are they going to take them along? Carry them on their backs? They have no choice but leave them behind.
The US hasn’t. Almost all of our social programs are aimed at the elderly; they’re the ones who vote!
Not even family might protect you: There is a German "Robin Hood" type that really existed whose biography I read. His children refused to let him in when he was old, they did not want to or could not share.
Living with family requires that they had the space, that the family had enough income, that they actually lived together (women especially were married off, if you only had surviving daughters you depended on their husbands).
Modern societies (especially the so called "ponzi scheme capitalist culture" ones) tend to go far beyond pretty much all past societies to support such people.