>Why would they care as long as the bills get paid

I imagine it's the cause of several support tickets along the lines of "I got hacked and racked up a $50,000 bill because of bitcoin mining"

They don’t ban it, but new accounts or even semi old accounts will have hard time getting access to more than a few instances. Most of the GPU machines are behind lock and key that go toward AWS bigger clients and clients with a proven track record. They don’t want to be stuck with an unpaid ec2 bill for a multi thousand dollar a month vm.

With AWS prices that must be burning money (if you honestly pay the AWS bill).

I didn't do the math, just my feeling.

It’s a magnet for credit card fraud: take a stolen card and create an account, run the mining until the owner gets the bill and does the chargeback. You are untraceable and Amazon is left holding the bag.