shifting risk to the creditors is the entire point of limited liability; the risk of deadbeats abusing it is always there, and the ability to pay is something almost every business will take into account when arranging a line of credit

amazon could completely negate this risk by requiring pre-payment for small/unknown operators, which is something a lot of people (myself included) desperately want them to provide.

I'm sure they've done their sums here, and have figured out the increased revenue from customers not being able to set a budget is more than their potential losses from deadbeats

the variable costs are basically zero, after all ( bandwidth and CPU time are worthless if not utilised)