I agree, but I also think that the ethics is just an excuse not to release the source code & models. The AI community clearly disapproves of papers without code. This is a way to skirt around that disapproval. You get to keep the code and models private and (they hope) not be criticised for it.

With Stable Diffusion I think they just didn't expect someone to produce a truly open version. There are plenty of AI models that Google have made where they've maintained a competitive advantage for many years by not releasing the code/models, e.g. speech recognition.