It’s because the incompetent PM made the visa free for mainland Chinese. It’s going to get a lot worse in Thailand.
The culture is the problem and the CCP insistent on keeping outdated traditions and social values keeps them in the past. China cultural values went to shit ever since the cultural revolution and the government has done nothing to better it, only doubling down and adding more problematic beliefs. There were needs to be selfish and to deceive for survival, but with the kind of government the CCP is instead of that slowly going away after the worst is over you have that continue to be ingrain into future generations to the point it becomes an identity. Then add the contemporary dose of propaganda and the sudden increase in progress and you have the superiority complex.
You must have never dealt with Chinese tourists. It’s not racism as much as directly observable behaviour of many Chinese tourists, especially towards other Asians or black people. It shouldn’t be surprising that many people in mainland China are radicalised, and it comes as no surprise that’s how they behave outside their country.