> It is a very reasonable choice: your plug-in project has grown to a scale you have never anticipated. Therefore, you built your own system from the ground up, one which you have total control over, instead of keeping to rely on someone else's system as you did before. This would make new features and bug fixes more easy to be implemented.

Exactly this. We ran against walls trying to realize our ideas with MkDocs' APIs, so a rewrite was due. With MkDocs being unmaintained for over a year, we took the initiative. Since we have excellent product-market fit, investing into a new stack was just logical.