It’s a nuance or what exactly you condemn. Being Israeli isn’t strictly a factor everyone can control and resenting people for their place of birth is unfair. Even if the two were perfectly interchangeable, the choice “Zionists” shifts the focus from “who” to “what for”. The repulsive trait is genocidal ambition, not nationality.

It’s also a question of scope: “Zionists” includes non-Israeli Zionists.