Firewall missing from AWS MarketPlace Centos7 image
Solution 1:
You get exactly the image the description says:
... built with a minimal profile ... The image contains just enough packages to run within AWS, bring up an SSH Server and allow users to login.
A reason not to enable/pre-configure any firewall is of course that it is not a requirement in many deployment scenario's and an image provides the most flexibility when people only need to add what they need rather than also remove what they don't...