Comment by bri3d

The biggest excuse is much more reasonable (albeit annoying, the same reason why most board support firmware isn't open source): ECUs are built using code generation from models (ASCET, LabView/Simulink, etc.) on top of 10 layers of proprietary middleware and compilers, using components supplied by hundreds of consulting firms, so an open-source effort would have to be a paradigm shift in the industry from the ground up. It's not something Porsche could decide to do on their own.