With the mass forward the plastic stick itself acts like tail fins. Like if you take a stick of balsa and screwed on a metal nut to one end. That moves the CG toward the nut end and the stick itself has enough of an aerodymaic effect with the majority of the area behind the new CG to stabilize the resulting "arrow".

The cup itself obviously has a lot of drag and side area of it's own but apparently it is not enough to make up for the effect of the dart's tail that is behind the CG and has a longer tail moment arm to lever with and ensure the cup stays dimple frontwards.

And for the sake of simplicity in this forum we'll forget about the effects of excess spit on the cup and the assymetrical effects that produces......