Even though you don't enable it to be shared people can steal you character skin. Why can other people make their own skins or use ones that are shared? Not ones that the creator didn't want to share with other to just keep to him/her self? Basically the people copying them are just wannabes or fan boys of that creator. People that don't know how to be >Original<.
Why are other people aloud to copy your minecraft skin?
Cry
Actually skins aren't owned by anyone. You can use the skin of whoever you want and say it's yours. Half these "wannabes" of the creators(I'm guessing you saw your favorite YouTubers skin being used, cry me a river), could have made the skin originally. Disabling sharing is also pointless, people can just view the skin and re-create it themselves.
The moral is, skins are owned by no one.
Seloje
Minecraft is about enjoyment, not getting bogged down in technicalities.
Does it matter whether they're wannabes or fan boys?
If the original creator of the skin had wanted it purely to represent themselves then the smart thing would have done to personalise it, or promote their own YT channel/website via the skin, but most people just make skins because they enjoy it, not because of the outcome.
Gameron