As big as amazon is, this could have been noticeable exposure, especially if they are partially self-insured and/or have other risk-sharing provisions in place.
Think: class-action lawsuit on an order of magnitude approaching asbestos.
I'm exaggerating a bit, but Amazon is wise to avoid total reliance on their position as facilitating a marketplace as opposed to being the seller. I don't think too many courts would toss a lawsuit over a newly vision-impaired 12 year old just because Amazon only got a cut of the sale as opposed to was the seller -- TOS provisions be damned.