The resource usage required to tank a small startup (that could’ve become a bigger customer later) is probably peanuts to Amazon. I’m not sure how often they do this (or whether they do it at all) but it would make business sense for them to occasionally grant “billing forgiveness” in serious situations.
Of course Amazon can sponsor those companies hoping that they'll bring more profits in the end. But that's not a guarantee, just a good will, may be depending on mood of support person who'll handle that specific case. I made a mistake with Amazon in the past which costed me $100 and I did not get a refund despite asking for it. I had some bad sour in my mouth, but whatever, my mistake, my money.