Well, my understanding of the system was that re-rolling unlocked a skin for you. Maybe you didn't have enough gold stuff for that GP skin, but with the re-roll, you don't need gold stuff. You just get the skin.
In any regards, it's random. You took the chance on a random roll instead of just breaking the skin for blue stuff and saving until you got something you wanted. That's the random part of it. You can re-roll into a free GP skin or you can re-roll into a super awesome expensive skin. If you chose that risk, you get what you get.
Also, why are you even complaining about a feature that lets you get FREE skins? Skins that normally cost money. Why can't you just be happy that you're getting free skins in the first place? You don't have to get any specific skin, so it's not like that's a problem. You don't like the skin? Break it up and hope for better luck next time.