Package and environment variables not set in workspace-full-image

My installation follows the guide: GitHub - gitpod-io/gitpod-gke-guide: Running Gitpod in Google Kubernetes Engine
The values.yml file is not altered, so I suppose the workspace’s default image is gitpod/workspace-full.

After starting the example workspace, template-python-flask, I found that the Python Env is not configured. The command pyenv is not available in the terminal.
Actually, pyenv is installed as described in the Dockerfile.

Then, I found that those environment variables set in the workspace all disappeared though, the softwares are installed as instructed in the Dockerfile.

Anyone with similar issues? How can I look into it?