Another nice thing about env vars is that they don't appear in the process table, unlike argv. For many applications, that makes them a suitable place to inject secrets, and makes them convenient to inject via wrapper tools.

For instance, the fact that the aws(1) cli tool and the AWS SDKs by default take IAM creds from AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, etc. means that you can write programs like aws-vault (https://github.com/99designs/aws-vault) which can acquire a temporary AWS session and then execute another command with the creds injected in the standard AWS_... env vars. For instance:

    aws-vault exec prod-read -- aws s3 ls
    aws-vault exec stage-admin -- ./my-script-that-uses-the-aws-sdk-internally

Also, passing arguments as env vars is part of the "12-factor app" design (https://12factor.net/config). That page has some good guidance.