[quote=@Gentlemanvaultboy]
Why would you limit yourself to only existing devil fruit?
[/quote]

I'm not the OP, so I can't really give a real answer. But the existing Devil Fruits are pretty interesting. 

Plus, it eliminates the chance of people trying to create overpowered Logia Devil Fruits or something.

That said, I'd like to express my interest if there's still space.