there is a very specific legal reason for that
A misguided or intentionally malicious reason, for what the effect of that law is. Codifying into law the conflation of Judaism/ethnic Jewish identity with zionism is itself antisemitic. Calling for the end of Zionism isn't the same as calling for the end of Jews or Judaism. What is the use of being allowed to criticize Zionism the ideology when you're not also allowed to advocate for its end?
"Zionism is a settler-colonial ideology." <- Ok "Zionism is a settler-colonial ideology, and Israel as a Zionist project should be dissolved in favor of a single-state that provides equal rights for Palestinians" <- Not ok, somehow?
The law as written only allows abstract and dissociated critique of Zionism, but forbids any criticism that comes too close to threatening Israel's existence as a ethno-nationalist state. That's a huge problem.
How dare we ignore the trauma of those committing violent oppression?!