Because the world is not simply 1's and 0's. There's a lot more to this than being right, including how to say that without coming off as being antisemitic. You can't just say things like that in our complicated world on complicated subjects on top of which she's a female Muslim congresswoman, who is already at a disadvantage in the system. Giving ammunition so the GOP can paint her as antisemitic won't help anyone, which is why politicians need to be skilled at not giving soundbites that will be used against them.
But she was talking about aipac and it's influence on Israeli foreign policy .
Everyone knows that. The alt right be damned , why does she have to cater to what the labelers think . If she is right she is right . End . Right ?
If she has to dance around criticism even for some on the left then the haters win.