This template used the deprecated SfdxCommand.

For new plugins, we recommend the generation commands found in plugin-dev. https://github.com/salesforcecli/cli/wiki/Get-Started-And-Create-Your-First-Plug-In#generate-a-plugin-and-run-the-hello-world-command

If you really want to start from a github template, use https://github.com/salesforcecli/plugin-template-sf-external (general use) https://github.com/salesforcecli/plugin-template-sf (a more opiniated template designed for Salesforce-owned plugins)