There is not only Kurds per se, there are many different fractions, Peshmerga, pkk, Kurdish Hezbollah are the main fractions with wings.
After the fall of Saddam Peshmerga/Barzani gained most, he also has the support from Turkey, pkk is against him officially because he is a dictator but in reality because he is siding with Turkey.
In Syria they are being used against isis, its very naive of them to think anyone in the region be its Assad, Iran or Turkey will allow ypg to have a separate state, everyone is just waiting till isis is finished, you can guess who is the next target of Assad and Iran once isis and rebels are finished.
Or lets say Assad looses then its even worse for ypg, either way they wont have separate state, they are being used once again, they just dont see it yet.