US doesn't want turkey and Kurds, fighting, already they are very famous for ditching states and terrorist organisations, after making use of them and finding no value, Pakistan is a clear example. We can hope that SDF has attained a no use status from US. Turkey is more of value than pkk, unless they have some extreme ideas. So they are exerting pressure on SDF to leave and at the same time requesting turkey, to soften a little bit, finally if SDF refused they will ditch them, and allow the Turks to have their way. US accomplishing their interests in Middle East with Kurdish forces is out of question, they need turkey. They needed a force at that time to fight without sacrificing their soldiers, and have their presence in Syria, where Russia and Iran too had their influence.