Or they can close down the shop if they can't find the money to do the right /required thing.
They would have said margins are too thin, that it's impossible to pay more, that menial labor doesn't deserve more, that paying more would result in immediate widespread layoffs, that warehouse employees have little recourse but to accept their lot or quit because that's just how the market works.
But that argument assumes Amazon, or any business, pays some objective measure of what a job is "worth", or as much as the market will allow. They don't, they often pay as little as they can get away with.
So yes, Amazon could close down the shop, but Amazon could always close down the shop. They could also afford to pay their warehouse employees more. They don't, not because they can't, but because they prefer not to.
It's not Amazon that creates this situation. It's the market system itself and it will always exist, because if Amazon doesn't do it some other employer will -- in some jurisdiction or scenario in which they can get away with it -- and gain a competitive advantage. Unless there's a labour shortage, or government action, it's a race to the lowest common denominator or worse. And that's why the formation of a union across the whole sector is imperative.