EA server issues are to blame
The Amazon page for SimCity will no longer allow customers to purchase the game, citing server issues as the reason for pulling it. People all over the Internet are complaining about their inability to play SimCity due to its DRM that forces the player to always be connected to EA's servers.
Here is Amazon's statement from their store page:
"Many customers are having issues connecting to the 'SimCity' servers. EA is actively working to resolve these issues, but at this time we do not know when the issue will be fixed. Please visit https://help.ea.com/en/simcity/simcity for more information."
EA has been attempting to fix its servers as quick as possible, even pulling certain features from the game in order to help provide more stability. The download is the only version affected, as the physical copy can still be bought from Amazon. Kudos to Amazon for looking out for the consumer.