I don't really have a beef with the Kurds per se, except that by allying with them in Syria we are causing friction with our NATO ally Turkey.

It's just another case of a proxy war, with the US using a made up organisation called the the SDF ("Syrian Democratic Forces") as a proxy to hold the oil fields, so the US can steal 90,000 barrels a day of Syrian oil (their entire output) and deny the Assad government any hard currency revenues.