Because they are poor, at least on average.

Yes, coastal cities like Shanghai have become spectacularly rich, but you know what, it was also spectacularly rich in 1895, in 1930, and in

1947. that didn't prevent China from overall being a disaster during most of those years.

China is a very big place with a very big population, it's going to take awhile for the entire society to build up enough wealth to be considered wealthy.

China now is basically at say.. Japan 1960 , Taiwan 1980 ish overall (though with considerably higher variation .) it's going to take at least another 30-50 year for China to be reasonably wealthy, that is if nothing goes horribly wrong during this span.