Primatologist Jane Goodall Asks a Powerful Question

I would say the answer is a combination of greed and tribalism.

We evolved living in groups, distrusting/hating people from outside our group who do not look like us, worship like us, etc.

At the same time, the socio-economic paradigm in the developed world of 1000 years ago, i.e., medieval Europe, morphed from feudalism to free-market capitalism, eventually giving rise to greed and, in general, indifference to the suffering of others.