Why is China less expensive to manufacture items, products?

Their labour costs are far lower than in the West, as is the living-standard for many people, but be careful.

We can not make simple comparisons or contrasts between different countries' pay rates for equivalent work.

What we may think as employees as a dismal wage in our land, may be thought by similar employees as generous in theirs.

What counts is whether you can live reasonably on what you are paid, by your own normal standards let alone expectations.

The real effect is that it does make goods imported from countries like China relatively cheap in the West. It does not necessarily mean the workers there are underpaid by their standards, though many may well be; but their overall costs are lower.