It does list cli plugins. The question remains, why it doesn’t show those located in ~/.docker/cli-plugins/.
I tried it earlier successfully by downloading a release from the github repo:
wget https://github.com/docker/mcp-gateway/releases/download/v0.36.0/docker-mcp-linux-amd64.tar.gz
mkdir -p "$HOME/.docker/cli-plugins/"
tar xzf docker-mcp-linux-amd64.tar.gz
mv docker-mcp "$HOME/.docker/cli-plugins/"