Because your stack trace should be more encouraging

Cloud Formation 

aws cloudformation deploy --stack-name CodeArtifact --template-file ./code-artifact.yaml --capabilities CAPABILITY_NAMED_IAM
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Waiting for changeset to be created..
Waiting for stack create/update to complete

Failed to create/update the stack. 
Really good try though.

Run this to find out more:
aws cloudformation describe-stack-events --stack-name CodeArtifact

Better luck next time!