1. The amount of leather you get from leveling skinning is nowhere near enough to level Leatherworking. Once you have leveled your Skinning skill to the point where the next skill-ups come from mobs that drop Medium Leather (for example), you have maybe half of the Light Leather you need to level Leatherworking, if that. The result is that you have to endlessly grind mobs that no longer give Skinning skill OR XP in order to scrape together enough leather to level Leatherworking. The other option is to buy it all on the AH, but that's not how it should have to work.
2. Once you grind up all of that leather, you make gear that is completely useless. The crafted items from 0-60 have never been changed since the original release of WoW. But the leveling process has been sped up, quest and dungeon rewards have been improved, and so on. The stuff you make while leveling crafting professions is completely useless to you, and nobody wants to buy it either.
The process needs to be streamlined, and the results need to be useful while you're leveling. The amount of leather/ore/herbs/etc required for the patterns you make while leveling crafting professions needs to be dramatically reduced, and should be balanced around the amount of those materials you naturally accumulate while leveling the gathering professions. The things you make should be useful, and it wouldn't hurt if the look of the items was improved from the 8 year old stuff still in the game either.