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.
I don’t remember where, but I read that a majority of modern Cuban migrants are economic migrants, so they plan on moving back to Cuba. Also, a lot of Vietnamese immigrants seem to be return to Vietnam for work. Although the stats for the latter may be outdated.
This doesn’t your answer because it’s just a single guy, but it is funny. I know someone whose boyfriend is a Chinese immigrant, and he despises china. I was expecting his reasoning to be they’re oppressive or censoring too much information, but no. His father owns one of the top automobile brands in china and was forced to pay workers more after Xi’s labor reform laws, so now they hate the government.