A twisted logic to serve customers

The other night my friends and I were looking for somewhere to have dinner. It was raining quite heavily. Then I remembered there was a restaurant nearby called Old Tofu. I've been there before for hotpot and I know the food is good. It was about two minutes away, quite long to walk in the rain, but our best option.
We got there in the end. It was empty as it was mid week and raining. The waitress greeted us and informed us there was a ninety minute time allowance on meals. This was quite normal for places during busy hours or when they serve all you can eat. This was neither. I couldn't be bothered to challenge her, as we just wanted to sit down.
We ordered a hot pot with a spicy soup base on one side and a normal soup base on the other. We also ordered a plate of beef slices and some other sides. They were doing a promotion, if you check in and make a comment on their Facebook page you get 50% off the next plate. That sounded like a good deal so said I'll do it first to show her, and order the second plate later on.
The meal went well. Food was good, my friends and I were having a good chat, service was prompt and courteous, and we had the whole restaurant to ourself. After we finished most of our food, I asked for the second plate of beef. The waitress said, "Sorry, your ninety minutes is up." The restaurant closes at 1am, it was 10.30pm and there were no other customers waiting for a table. I'm not one to throw my weight around, but I shot her a stern cold look. She backed down and said "I'll bring you another plate of beef" rather timidly.
You know sometimes you're not hungry, but not quite full yet, and is just missing that little bit more food to complete the meal. That's how we felt. When she bought the plate over, she explained that since there were no other customers, they would be closing earlier than usual. Now, that I can understand if she wanted to leave work early. What I was annoyed with, was I was still mid way in my meal and she's trying to put a sudden halt to it. If she had said upfront, we're going to close early tonight regardless , I'd be fine. But she was hedging her bets. She told me I could only eat for ninety minutes. I expect if there were more customers, they will stay open. So where's the logic to that? Is an existing customer already sat down worth less than a new customer who walks through the door?
Anyway, we finished that plate of meat, leisurely I have to admit. Paid our bill and finally left. No hard feelings since they have a rather fierce looking statue by the door.
Restaurant Information
Old Tofu Hotpot

No. 299, Section 3, Dongxing Road, Xitun District, Taichung City, Taiwan 407
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