Reputable tailors/ shirtmakers buy from Mills/suppliers that they trust.
I know what I will get, buying 120/2 broadcloth from alumo.
I don't know what is showing up from Chinese supplier with supposedly the same construction.
Some of the Large mills, with name recognition, are playing also sorts of games to cut costs.
weaving in lower price countries.
Playing with constructions.
Using chemicals and resins in finishing to cover up the use of inferior raw materials.