Though to me, whenever I have been there, especially California, it looks more like the American South before the Civil War, with poor people doing bad jobs (people with broken arms at the cash register, Mexicans doing hotel rooms or people 70+ years old packing groceries) and rich people in big cars driving around with an oversized cup of coffee. There is the rich elite and the servants.
So this is why people say this.
The changeover happened in the early 1970s. The Powell Memorandum spells out the political program enabling it. Starting in the '70s, while the GDP has continued ever upward, middle income leveled off, and has barely risen since. All of the difference has been carefully diverted into the pockets of the 0.1%. Now the US has many billionaires and many, many millionaires, and "the rest", who are what is called a "managed population", our apparent collective consent to all this carefully curated.
Rebelliousness is channeled carefully into increasing the divide. The radical increase in fortunes of billionaires over the past four years is always blamed on something about COVID, not on very deliberate policies enacted by the government in power at the time.