...women buy sweater dresses to wear when it's cold. They should almost always, therefore, have long sleeves.
If retailers want to offer a variety of sleeve lengths, the proportion should be something like this: 3/4 long sleeves, 1/4 everything else (combination of short sleeves, 3/4 sleeves, and even the occasional sleeveless sweater dress.) Instead, it's often the other way around, which is truly baffling.
First off, when you put a long-sleeved layer beneath the dress to keep your arms warm, you pretty much change the look completely.
Second, that long-sleeved top gives you a big, thick "panty line" below your waist that's hard to conceal in a sweater dress since knits do cling.
And that is my sweater dress rant.