I can't say 100%, but I think they have a policy of leaving very little extra material in trousers for future alterations.
When I bought them, the saleswoman told me that the pants come with unlimited future alterations. However, when I look at them now, it looks like there is less than 1/2 inch of material. Basically, they are trying to set you up so that if you gain 5 pounds, you will need to buy a new suit.