Amazon is valued at $1 trillion but Amazon does not have $1 trillion. Amazon's total assets are only about $131 billion. $20 billion of that is cash.
Moreover, it stands to reason that much of that excess (beyond assets) value is predicated on their unit economics, which depend on fulfillment costs, remaining good.
> only
"Only" as in an order of magnitude less than originally estimated.
So they have plenty of money not to have to choose.