Most of US cotton is used around the world for fabric production.
What happens here as there is very little mill left is
The cotton is grown in the US
Shipped to China
the fabric made in China and then shipped to where ever the orders are.
There are also lots of other countries that grow and produce fabric. Mostly in the middle east and east.
Why it may be more expensive for others is a whole host of reasons
First they have import/export duties, taxes and tariffs that we in the US do not have or are cheaper.
Second a lot of those countries have high taxes and or VAT
that can add an additional 10-20% over the base cost.
Second the min wage is higher in some of the countries so the over head is higher.
You have a trade off.
We in the US expect and almost demand cheap prices and that has lead to us importing and owing China more and more.
Other countries may feel that is not what is best for their citizens and they have instituted high taxes and other programs that they believe will help rather then hurt