I have tons of Mogas I don't want. I assume everyone else does, too. And with the system in place where you can get some Mogas only through Moga cash, I'm sure there are people with an overabundance of some "Premium" Mogas, while they are missing some other, more basic ones. It seems logical, anyway. Almost every other monster taming game has trading, it's a staple of the genre, especially online. Instead, there is little interaction between players, unless you include pvp.
For me, it's more personal. I did the 30 Moga cash spin and got a Harayama. It's a Rare, not even a Super-Rare, and not even from the Premium page. I felt so ripped off. If I released it, that's 30 Moga cash down the drain. But if someone wanted to trade for something else, it wouldn't be a complete waste, see?