The sticks normally don't make ROI. They are only to test mining and have fun.
A antminer u2 costs about 20$ for 1.6 GH/s that's 12.5$ per GH/s.
While other miners cost 1-2$ per GH/s.
Well, that explains a lot
And yet, I see a lot of people have made some massive USB mining farms. I guess they too are also "having fun"