Well, I think it depends on where the restaurant is. If it’s in a small town in China, most people would be impressed and try to talk to you in Chinese. But if it’s in a big city in China, people might prefer to speak English to you. Moreover, if it’s in other countries, Chinese people living there for a long time might think it’s more efficient to speak your language. Other possible situation is that to certain people languages are hierarchical. They might think it’s more proper to speak your language there. But, I am not the waiter/waitress, so I don’t know what the real situation is. If you know Chinese people there, you could ask them.
As for why they don’t correct you. Let me give you my story. I once worked in US for half year. My English wasn’t always grammatically correct, but people still understand me. During that time, no one corrected my English unless I asked them to do so. It’s doesn’t mean that it’s rude to correct people. It’s just because that people are always kind to foreigners speaking their language. They tolerate mistakes because they can understand you. And it’s the same to Chinese people.
Keep trying to use Chinese in your daily life. There must be someone willing to interact with you in Chinese. And once you find them, your Chinese will be getting better!