Hardware cost money? The rate at which AWS buys more hardware is consistent with their income from their cloud rental business. If they're not going to buy the hardware otherwise, then evidently at cloud market rates the marginal income isn't worth it.
Hardware, rackspace are all resources. If something is using up hardware and rackspace, there is opportunity cost.
If they cared about saving money they would try to sell it. Something which doesn't bring many millions is to small for Amazon to care even if it cost rounding error on a balance sheet to run it.
The problem is that at a big/huge company, every little project imposes some share of costs and distraction all the way up the line and on supporting groups. And, yes, that means something could be reasonable as at least lifestyle business for someone. But unless it more than incidentally supports more central parts of Amazon's business, a million dollar side business isn't really very interesting to a company like Amazon. And have more than a few of those and people start to reasonably ask what Amazon is actually focused on.
Hardware, rackspace are all resources. If something is using up hardware and rackspace, there is opportunity cost.