Because if you spend enough time on the internet, especially the Western side, you start to hear voices of people who oppose their governments and not enough from those who support it.
Even many who are supportive tend to say that their government is authoritarian.
Thanks for the ping @GrainEater@lemmygrad.ml .
Chinese in China here, I think a better question than "Do you support your government" would be: "If the US government were to replace the CPC and current government tomorrow, would you approve?" Sorry to folks in Nordic countries (another stereotype propelled by liberals) because the US is the "beacon" that liberals use mainly.
If people from any country have no experience with living in other countries, they might be more inclined to topple their own government if their living conditions aren't great and someone were to advocate for the toppling. Even if people read about how bad some foreign governments are in the news, some people would just brush it off as "propaganda", they would have to see it for themselves to believe. This goes both ways for both the people of the US and China.
Comparison is a powerful tool, but some people whip out the "whataboutism" card when you try to do that, they tell you to address the problem instead of finding worse examples from other places. Indeed it's always better to address the problem at hand, but people who scream "whataboutism" in relation to China's issues are really saying "don't look at worse places to make yourself feel good, overthrow the SEE-SEE-PEE regime now!"
Do I support the CPC and Chinese government? Yes and yes.
Does China have problems. Yes.
Do I need to hear from egotistical maniacs in other countries on how to handle issues in my country? No.