I think a big part of it is that most (recent) mainland expats still mostly consume mainland (i.e. censored) news media and social media, and their friends in their destination country are almost exclusively other mainland expats. Reading and writing Chinese is significantly more comfortable for most expats and mainland Chinese media has cultural appeal for them as well for obvious reasons.

It takes an unusual and frankly relatively rare amount of independent thought and personal research to believe something at odds with a reality that your entire social network accepts as obvious fact. Especially when you start from the same manufactured reality that they did. And I would guess, even among expats, speaking about such doubts of the official CCP line probably is met with significant resistance among other mainlanders as mainlanders tend to be relatively nationalistic (as a product of their censored media and “patriotic education“). Why bother with it then? Which is also a part of contemporary Chinese cultural (no doubt nurtured by the CCP) — politics are is the business of the government, not the governed anyway.

So, in short, there’s a lot of political inertia for mainland expats, not a lot of incentive to consider other views, disincentive to adopt other views, and a lot of work to learn about other views anyway (must be in English in non-work hours, learning a whole alternate history and political philosophy takes a ton of time, your network of Western friends with sufficient knowledge to discuss these topics with is probably amounts to zero). So really, it would almost be more surprising if they were flipping views — even though, personally, I’ve spent significant time learning the CCP canon and find it rather obviously holey.