I live in a smallish east EU country whose PPP is supposedly double that of nominal GDP, yet whenever the prices I'm expected to pay for a Corolla, my shopping in Lidl or a Macbook are largely the same as what I would pay in Germany (as is expected from a customs union).
Even restaurant prices don't match the differences.
The difference probably the Germans don't go buy at cheap stores like lidl. The easy way to do PPP is to go by how much people pay and not how cheap you can get something for, which gets you a much less accurate picture of how much it actually costs to live there.
That being aside, I mentioned Lidl cause they sell pretty much the same stuff in both countries. As for PPP, it's supposed to be based on a basket of goods, which is supposed to be as similar between two countries as possible.
Comparing lower quality products in country A to better ones in country B would tell you nothing.
If your average Chinese person lives in a comfortable, well-built apartment that costs 1/4th of what it would cost in the US, drives a car that's similarly built but cost $10k instead of $40k, and eats food thats the quarter of the price, could you convincingly state that he has the quarter of the actual wealth, even though the numbers would indicate that.