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.
These countries don’t get polled much, so it’s hard to get a number. There’s that famous Harvard survey showing extremely high satisfaction with the Chinese government though. Opinions on these countries are going to lean negative within the western internet ecosystem. For example, the vast majority of Chinese people are posting on Weibo, Douyin, Xiaohongshu, etc. etc. rather than Twitter, Reddit, Youtube, and Facebook.
There’s a few Harvard polls, but I recall one saying at least 70% of Chinese people consider china democratic, vs around 40% of Americans consider the US democratic. Now perception and reality are different, but if a majority of people see that their demands are being turned into policy (or the opposite, their demands being ignored), then certainly there’s some truth to it.