They were USA allies, you don’t just desert your friends like that.
Eventually USA should have left Syria, but not like this. Trump had a right idea, but he did it so wrong that the result is worse than it was before.
Now Syria will destabilize again, Russia will have more power in the region and Europe will be weaker bcs of refugees coming fear of ISIS.
USA should have started to support Al-Assad now that he won the game. That would have pushed Russia, Iran and Turkey out.