1. They keep changing the hidden setup prompt to prevent abuse and such. For me it insists on providing sample code and saying "this is just an example". I used to be able to tell it "write production-grade code" but it seems to ignore that now.

2. They fine tune the model. When you do that it tends to overfit on certain things, causing them to have more "weight" and others get pushed back. creativity suffers.

Those are only my thoughts, can't confirm anything.