This item costs less than E-bow because:
A: It is purchased with CP, where E-bow is a rare drop from the NM Eastern Shadow.
B: This bow is 16 levels higher, at 55 nothing rivals E-bow, but as the levels get higher other options become available (O-bow, MC bow, Hellfire/+1, Selenes bow, Gendawa+1).
I'm sure there are more reasons, but these are the first things that came to mind.