I have noticed this aswell, even when you do not Rank up the experience goes down with every craft. My guess is that this is part of the fatigue/surplus system to encourage you to break away from mindless repetitive grinding to a more diverse leveling system.
Once i found out i realized how much i enjoyed to travel to different fishing spots and continents to get fish for leveling my cooking. As an example:
1. Salted Cod (Limsa Lominsa)
2. Grilled Carp (Gridania)
3. Grilled Trout (Ul'Dah)
It seems that they bring a lot of the lessons learned from FFXI into this game. Recipes to level up your craft, because they where cheap or easy to get materials for, influenced the whole economy. Not only that, they also influenced which mobs where farmed almost 24/7.
It took me a while to realize that all these things that do seem like restrictions at the first look, actually are giving you a new freedom and create an almost sandbox like economic system that has no restrictions to grow.
Merchants will carry a much more diverse assortment of goods at all prices as opposed to the classic MMO approach where you will only find very few items every level range beeing mass produced.