Why does clothing that is supposedly the same size differ from one manufacturer to the other?
They all have their own fit models they work off of. They may be the same size technically but when you “FIT” something to them it will come out differently. And when they cut and sew the items, they can come out different even within the size. If one Size 10 doesn’t fit but almost, try another. Same with shoes. Fabric from one bolt to another can also stretch different.