Allowing the Court to selectively strike language from and initiative would make legal the Courts legislating from the bench. Imagine how easy it would be to alter or even reverse the intent of a law by striking a few words. The Court needs to strike all of Prop 22 not just specific language. The specific language was what the Court declared made Prop 22 unconstitutional. Once Prop 22 was declared unconstitutional, according to the court, there was nothing preventing same sex marriage.
The courts can legislate all they want because the other branches have ceded unlimited power to the courts.