5th

3. Branding: chances are you're buying from a branded store (unbranded shorts are actually very cheap). And you buy from them because you trust them and like them. You wouldn't mind paying the premium to have a good pair of shorts you like.
4. Pants and shorts are replaceable with each other. If you don't wear shorts you wear pants etc. So no loss for the business if they're priced the same.

I'm not an economist so pardon my lack of knowledge. From what I understand about the supply and demand model, in a free market the supply and demand will reach an equilibrium i.e. price will be very close to cost. Unless there is monopoly, price jacking, government policies etc. As far as I know, the shorts industry and the pants industry operate in the same economic environment. So cheap labor is available to both shorts and pants industries.
Personally, I think that the supply and demand model doesn't explain this phenomenon well. It's better explained with customer behavior.
1. Price sensitivity: when you're already paying $50 for something an extra $5 wouldn't make you stop wearing shorts so most people just buy it.
2. Convenience: if you're already buying a bunch of clothes, you wouldn't bother to travel to another shop just to save $5 on a pair of shorts.
(continue...)

More specifically, the cost of shorts is same as the cost of pants, therefore their price are the same.

A well fitted t-shirt and well-done hair. If you were poor you would be wear your sibling's clothes that would fit you for another 5 years. And your hair would look plain because who cares about looking good when you're poor.

Or the dead bodies

This isn't racist you dumbass

Just blame the dog

But I really c what he did there