It looked cute.
Apart from that, it's a bit of a form follows function issue that also tied in with the design 'fashion' of those days. The luger pistol has a lot of design features that can be attributed to the Jugendstil / Art Deco style of those days.
What also influence the design of several luger parts was the request by DWM to Georg Luger to keep as much of the Borchardt design as possible, in order to reduce the cost for retooling.