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.
When I was in China, the city I was in was noticeably nicer than US cities. Quality of life seemed consistently good, as in, most of the city looked like it was in great condition and you didn’t really have any place that was a “bad area”. Even in places that appeared lower income (older buildings) were still nice and everywhere felt extremely safe. It wasn’t uncommon to see young kids walking around the city at night time unsupervised, and this is something I don’t think you’d see in any US city. From what I gather, there are maybe some complaints about things like media censorship, bureaucracy, and discrimination, but in terms of material conditions, the Chinese people seemed to be doing pretty great (at least in the cities). Better than a lot of people in US cities, even, so I can see why they’d be satisfied with the government’s efforts to advance the country. Then again my experience was a very very small window in a country with over a billion people, so keep that in mind.