Why people don't make bi-directional code/modelling programs

There's a bug in Draw.io that means a call to app.editor.setGraphXml(app.editor.getGraphXml)) isn't cleanly reproducing the diagram. I wonder why that is, possibly there's additional processing or cleaning on either a full file load or write. Individual nodes (proto MxRectange, MxCircle) appear to be recreated very well, but their relationships aren't (represented internally by both a top-level node in the model, as well as an additional object referring to the top level as a property of the sender or receiver in MxNode.edges). The closest example of what I'm trying to accomplish is swimlanes.io and dbdiagram.io - both amazing tools for taking something defined as code (giving developers all the power of cut-paste etc, as well as uber-easy readability and updates) and producing something visual from it. Interestingly, they focus on code as the input method, both right hand sides (RHS) are essentially read-only. I wonder, why is that? Looking at Draw.io for a few hours, to the point whe