Because such a ban would also prohibit all forms of “Kiruv”, which, as seen by the hiloni ruling class, involves socially undesirable Orthodox Jews conducting missionary activities aimed at non-religious Israelis. To most secular Israelis (who are atheists, and very committed to that belief), the Christian missionaries are non-threatening and more amusing and deluded than anything else whereas the frum “missionaries” have a serious record of causing many Jewish youth to go off the zionist derekh and embrace the “yoke of Torah and Mitsvos” (the “yoke” which the zionist anthem sings about being free of). We should remember that to frum Jews, who accept the existence of a creator, the Christians are at least “serious”, but to most secular Jews anyone supporting the idea of a “creator” or “ruler” of the universe is totally off his rocker.
Most secular are not Atheist, but rather NON-RELIGIOUS as opposed to Anti-Religious meaning they arent against reglion in general, jsut that they dont want to be religious