Why make your projects properly open? Sustainability
The answer is sustainability. IKS is an EU-funded project which will eventually end. Proper project governance handled together with the Apache Software Foundation can help the software to survive and thrive for long after that.
Sustainability is something that is critical for all libraries and infrastructure software. If you want adoption, you need to ensure potential users and developers that the software will continue to be around. The way to accomplish that is to have a clear, open governance model. It is time to stop throwing code over the wall.