I'll venture an opinion as a "dirty furriner"
Americans are often more uncomfortable than other nationalities with talking about or acknowledging classes. It seems "undemocratic" or pretentious to say there are different socio-economic classes of Americans.
But, there are. (some would say increasingly so but I'm not sure I agree with that)
It is true that western countries, like the US, have very high levels of social mobility but acknowledging that fact also acknowledges that there are different classes to move between.
For my part, I come from a poor-ish rural background (I literally had **** between my toes on the family farm until age 16).
But, I went to a technical college (like my immigrant father did) and am more or less a "grey" collar worker (and small business owner). So, from the peasant class
to the boringly middle class
.
My sister also followed the same route but my brother went for multiple degrees and professional designations and made many, many millions and is definitely upper middle class.
One class is definitely not better than the other nor do they come with any inherent moral superiority. But pretending they doesn't exist is kind of dishonest too.