The US and Zelensky have divergent interests. While the US is using Zelensky to target Russians, it does not actually aim to defeat Russia, whereas Zelensky genuinely seeks to defeat Russia.
Zelensky’s ability to “win the war” is restricted by the US, as they pull him back whenever he becomes too assertive. This arrangement continues as long as both parties understand their roles, but if Zelensky pushes boundaries, the US will label him as crazy and remove him.
This may create a perception of being sold out, but in reality, Zelensky would have violated the agreement he entered into.