What was pizza when it was invented? it was the fast food of the Italian proletariat. Most of the "true Italian pizza" you can find nowadays is going to be from an expensive bourgeois restaurant, or rarely from an actual Italian family place if you're lucky to live near one. "Authentic pizza" is mostly not consumed by members of the working class, so how it could it actually be a real example of that culture?
The working class isn't a culture, it's a class. There are many different cultures that are present within the working class, including Italian-Americans. Find areas of the United States with large Italian populations, and you'll find those cheap 'authentic' pizza places, where working class people still eat. If you're asking why ethnic or traditionally working class foods are co-opted by the bourgeois establishment, the answer is just profit.