actually, even though the inseams are longer, they are not cut for a longer leg. first off, 34 inchs would only work on a 6ftr if she was wearing sandals/ballet flats. even when i do buy a pair that is 37 inches long, the knees are placed on the leg as if i were 5.7, and usually bunch around my knees and lower thigh. that is one reason why widelegs are great. that sort of thing isn't an issue.
maybe expensive brands don't want to cut off a segment of the population? maybe its cuz statitically tall people are wealthier? I think it is similar to high end shoes often being available in odd sizes.