What's to stop any open source containerizer project - or any other open source project - from starting a paid option? Nothing, as long as they don't violate the existing open source license. In that case there's an option to keep it free as in freedom. For project XYZ, a fork to to 'LibreXYZ' for example. IF there's enough community to support it.

Community support is always the question. If there's not enough community to keep the open source effort viable, then it ends up like Odoo (as just one example).