Actually the profit issue in this particular store is simply supply inefficient. Your can not expect to supply so many stores in so many cities with just 1 factory line to each product. When linking to a source, remember to check if the red bar (demand) is higher than the yellow bar (supply), otherwise as you can see in the picture, purchasing and sales units are just empty and idle doing nothing most of the time. If you detect a unit is under-supply, you better find a source that actually can supply products. (in you case, you would need additional factories/farms for all your products)
The brand rating issue, a particular media firm has a "limit" of exposure depend on the budget you set (it's what CPM means, spend less, less customers are exposed to ads, and higher the CPM price, cost more for each customer exposure at one time), and also the media firm's rating points will set a hard cap of how high the portion of customers can be exposed by this media firm (even if you pay the max advertisement). Usually, if your product quality and price is good enough, the loyalty will arise slowly over time when you have enough market share (you can think of it like a non-media advertisement, where market share is the "rating points").
As to how "low" you can set the rating and not hurting the brand loyalty,
in a previous discussion, David said the price does matter. From personal experience the threshold is around 30-40 rating for normal products at 30 quality (pasture products usually a bit higher than 40) at normal local competent, the lower the quality the higher the rating has to be to prevent loyalty drops. And since it's also related to local rating, if the local rating is low enough, you can also get away with low rating, if local rating is high, you also need to set it higher. For newly developed products without a market at all, it's even conceivable to get away with -100 rating (obviously there's no local rating to begin with, however the demand will be very very low, and not a long term solution when AI catch up in tech)