Many don't even do it intentionally, they just don't grasp concepts like Historical and Dialectical Materialism, which requires reading lengthy books to fully grasp. They may be anti-Capitalist at heart, but without a solid understanding of theory they play into bourgeois hands.
There's also the fact that the ideas held by society are a reflection of the Mode of Production.
US did offshore no doubt but it was not a vast majority. You can check the numbers, there was some decline in employment but US has high tech factories and industrial base is now growing quickly even with job growth since covid.
The reason it is largely a service economy is due to growth in service sector after industrialization. Once people got all their needs with goods met, they started buying service.
Think about all the food joints we have now for example. This is fairly recent thing. Sure food out always existed but not like this.
Also, people have god walkers, people buy insurance etc all this is kinda recent in big picture thing
I am aware of the process, the US produces the vast majority of its commodities oversees before "finishing" or "assembling" in the US. It's Imperialism in action, where it hyper-exploits the Global South for super-profits.