While understanding their motivation to combat fraud they have a 20-year purchase history and have already established identity through payment methods. This is just lazy and perhaps additional data harvesting.
Amazon got so large they stopped paying attention to the details.
Fraudsters almost certainly gain access to old accounts specifically to "buy" that trust and then farm it for their own uses.
I wonder how much a 20-yr old Amazon account is worth on the grey market. Mine is about that old, and I have – legimately – returned thousands of dollars worth of goods (that were faulty or just didn't work the way I liked) and it is probably very difficult for Amazon to distinguish between my legitimate returns and a hypothetical alternative where I'm a fraudster that just purchased this old account and am laundering broken electronics through the returns system.
Amazon got so large they stopped paying attention to the details.