Because it's much more profitable for Amazon to offer GPU computing for companies rather than mining themselves. A single P100 rate is $4 for hour. Such a rate would be impossible to reach with mining.
Dec 11, 2013 And, indeed, if you look at the table of Litecoin mining hardware performance, you'll see that this trend seems true. The AMD Amazon gives away $100 AWS EC2 credits to get people hooked. Mining worldcoin was a nice compromise - it stayed more profitable than Litecoin for most of my experiment.