It's a v good question. I'm tall (5'9'') and large (generous 22) and have never figured out why most retailers assume that, if you're a large size, you must be short with tiny legs and waist to crotch measurement - as well of course as having had a taste/style bypass.
Makes no sense, as BS says. Nor do you see many of these practically spherical women around. WHY do they do it?? Disappointing that none of the gurus Gigantaur asked replied.
On style, though have a few bootcuts still, prefer straight legs at moment. Above all HATE baggy, clown-like trousers, which is another thing some retailers think large women want!!