They get it from senior management, and pass it down like generational trauma. This was a problem even in 2013 when I worked there. Once, I was new and actually pushed back against a Director level person's poor behavior in a 70 person meeting, because I didn't know better. I was approached by multiple individuals afterwards telling me how "brave" it was of me.

At Amazon, unkind and downright unprofessional behavior by people higher up the chain is normalized, and has been for a very long time.