The vast majority of them are just fine, like with most tourists. The problem is there’s just massively large number of them in many tourist destinations compared to other countries (at least where I live), which means you more frequently see one acting poorly too.

The Americans are somewhat the same, we also get a lot of them.

That being said, even though most of the issues are because of sheer numbers it doesn’t mean there aren’t a few key cultural differences which can play a role in western locations being offended by Chinese behaviour.

The big one with China is that culturally there’s no expectation that you treat a stranger respectfully, the person you’re dealing with needs to earn your respect rather than having it by default. This comes across as quite rude to many other countries when you only have a single interaction with this person.

This isn’t a Chinese only issue though, Americans can also be quite rude depending on where they’re from and how they were raised, a good chunk of them are entitled assholes who think the world revolves around them when they visit.