The worldwide disdain arises from what you said, the additional association with communism / cheapness, and the fact that they are mass produced, generic, and boring, and no one wants to spend a lot of money to get generic and boring.
The reasons must be different.
McMansions + perfect lawn in a suburb full of curves and crescents; and various kinds of "luxury" cars, big TVs, etc. All things just out of reach of many of our middle class parents or grandparents. So now you've made it when you have it... until you look close and see there's no actual class differentiator in it, no taste to it, no art to it, or any particular advantage to it...
Just my, like, opinion, man...
The problem is really the combination of all 3 factors. McMansions definitely make people think the inhabitants have no taste, but they don't make people think the inhabitants are poor. Buildings that look like public housing make people think the inhabitants are poor, which is worse for a lot of people.