I mean, that just isn't true. There are amazon tribes today where they just send them down the river to die... your ideas are a disney-fied version of a false past that never existed.
Unspecified Amazon tribes don't represent the lion's share of historical treatment of aging populations. One negative example doesn't undermine the point.
Yes, humanity is full of various societies that do things differently. These ideas aren't disney-fied - they're just accurate representations of the fact that people care for each other, most of the time.
I appreciate your anecdote, but here's a few counter-examples: