Let me go through it for you.
Disclaimer - I have knowledge about clothing manufacturing, but I don't work for jiberish.
1. the material itself
This isn't regular shitty ringspun cotton. It's thicker, better made, more quality materials. To get all these different materials in limited quantity, you have to go through suppliers that cost more (because of the quality) and pay top dollar. Producing a limited run like jiberish does actually costs more because it's way cheaper and more economical to order in massive quantities, if you can move that much product. Plus, some of their material , such as the patterned sweatshirts, are specially produced for them.
2. Cut and sew -
To make product that isn't screenprinted american apparel blanks, you have to go through a cut and sew company. To do this, you have to work with them. Consultation fees are charged, anywheres from 30-60 dollars an hour, then once you have figured out what you want, they charge you up to 100 an hour to make patterns. If the patterns aren't what you want, you have to spend more money for them to fix them. THEN, you have to get all your material delivered to them, and pay them to make blanks.
Jiberish uses several methods to get their designs laid down some of which happens to the material before the cut and sew people get it, another expensive step. Screen printing isn't cheap on it's own, and they aren't using any shitty printers. If you want your print to last, you have to use good inks, good screens, and people that know what they are doing - which isn't cheap. You're looking at 2-5 dollars a shirt, which after cut and sew and everything else, adds up.
So, in short, although it seems like they are making a ton of money on 34 dollar shirts, compared to your whatever brand skateboard shirt from CSS you can get for 15-20, the profit margin isn't that high when you get into such a quality product.