I guess it's so the undershirt doesn't show under the outer shirt.
However, is there a style of outer short-sleeve shirt with shorter sleeves like an undershirt ?
Obviously you couldn't wear undershirts underneath them, but that's not a problem.
Most Helpful Guy
You can get shorter sleeve shirts, they're just a little less common, try looking at brands that have slimmer cuts, they're more likely to.
Also make sure you get shirts that fit. Tons of guys walk around with a shirt that's too big - the sleeves look long because the shoulder is overhanging by 4".