You may be right overall, but that's a particularly bad example, as Frozen simply eliminates the "flask" portion that gets deployed to the server in lieu of static files, ergo obviating the need for WSGI altogether.
Serving a Frozen app on lambda means serving static files on lambda, which is very doable, and a very different use case than developing something like an API to be deployed to lambda.
Edit: Re-reading our comments, you may be confusing the difficulty -- it isn't in building the CLI for Flask, it's in getting Flask to be served over lambda. Presumably, the OP could easily re-write the deploy functionality to deploy a flask application, it's just that the flask application is unlikely to work because it defaults to WSGI, which lambda (apparently) does not provide.
Serving a Frozen app on lambda means serving static files on lambda, which is very doable, and a very different use case than developing something like an API to be deployed to lambda.
Edit: Re-reading our comments, you may be confusing the difficulty -- it isn't in building the CLI for Flask, it's in getting Flask to be served over lambda. Presumably, the OP could easily re-write the deploy functionality to deploy a flask application, it's just that the flask application is unlikely to work because it defaults to WSGI, which lambda (apparently) does not provide.