You put it better than I could. Now, one might argue that many of the other attack surfaces are necessary byproducts of markets they want to operate in, and so

You put it better than I could. Now, one might argue that many of the other attack surfaces are necessary byproducts of markets they want to operate in, and software development isn't a market they're profiting from, therefore they shouldn't unnecessarily open themselves up to potential litigation. However, given how much so many other large companies already contribute, publicly, sometimes to the very systems Amazon may be using, it does seem a pretty hollow claim. If some of Amazon's system failed because of some patch that Google contributed to project X, would Amazon's first reaction be to sue Google?