Probably because its cheaper to make a sample thats sleeveless (less fabric, less kaam). Plus unless you have arms like those models, a sleeveless bridal is just going to look bad. At least, short sleeves suit almost everybody.
I don't know, I agree with you and thebear bc I think sleeveless AND short sleeves are for people with slim arms. It depends on the type of short sleeve, but cap sleeves for example are really fitted and...I dont know how else to put this, but your arm fat just kind of spills out of it. The worst is when people wear baju bands on top of that. In my opinion, 3/4 or long sleeves suit everyone.
Fitting issues aside though, i think sleeveless is a bad idea because people pay more attention to the show of skin by the bride than they do to the outfit and look.