I do not know if this is a bug or an intended feature, but if it is the latter it renders all food-focused businesses in the newest pack completely unviable.
In attempting to create a bakery today...
Ideas
aI'm having this same problem. I started a bakery yesterday with a coffee bar. The Sims buy a lot of from the coffee bar, including the treats that you can get from a coffee bar, like cookies. But the bakery goods on the shelves, they sometimes browse them but then choose not to buy most of the time. My Sim is rank 10 cooking, everything is excellent quality.
When they do buy, they buy the whole thing instead of just one, for barely any money. For the pizzas on the Home Chef Hustle table, I had slices of pizza selling for 1,000 simoleons, now they buy a whole pizza for barely anything.
I did learn you can have a food sale on the lot while the business is open. So I have one family member run the coffee bar, and one family member run a food sale, and one family member baking. It's a temporary workaround, at least.
Edit to say, I have had Sims buy the entire number of servings, but then also sit at a table and eat one. Once with a whole tray of cupcakes, and once with a whole tray of candy.