Do you really want two bike frames bouncing around in the same box, potentially damaging each other?

Shipping a heavier package costs more, shipping two frames safely requires significantly more packing (costing more), and it's a lot more work (time=money) for a great guy who's hooked us up and is making all of $2 per frame off of this. In the long run, it would cost just about as much to ship them together as separately.