I think it’s that the regional restaurants in residential neighborhoods have to broaden the menu to please everyone in order to stay in business. So while they may still have some excellent regional dishes, they may be harder to locate because the menu reads as generalist.
See this earlier discussion of protein + sauce (not unlike the mix & match protein-curry discussions elsewhere including here) – at TriDim Shanghai, for eg, there are certainly plenty of Shanghainese specialties, but also lots that are generic people-like-to-order-these dishes.
