[intopieces]

>Though I don't fully understand their ridiculously long trousers.

As others have pointed out, they hem them for free. This is a clever bit of optimization for them, for two reasons:

(1) Fewer SKUs to stock. Each type of pant only varies in waist, not length.

(2) The pants become non-returnable after alternation. This reduces the number of items that can be returned substantially, since very few people fit the dimension of the pants.