Hi all, same issue here. My city had a huge demand for commercials till about 350k sims, after that point (together with a big increase of population i put a HUGE amount of parks and unique builfing as well) the commercial demand is ZERO even if now i have 470k inhabitants.
I'm trying now to dezone ALL the commercial areas but still seems they don't need to buy bread, food, and clothes (i guess my citizens walk around the parks eating grass and dressing with leaves).
I have no traffic jam at all, plenty of trains moving stuff all around (most of them for export of course, since my commercial is totally abandoned and slowly closing).
Furthermore i have all kind of industries.
Next step, i will try to delete all the parks, quite sure that is the problem.
clearly THIS IS A BUG (i've never seen a city without any shop).