According to most Christian sects, the Jews “cut a deal” with God that lets them do their own thing, indifferent to the religiosity of the rest of the world. If you’re a Jew, Jesus doesn’t matter, you’ve already got an “in” with God.
Although Judaism is chiefly a racial religion - Israel, for instance, exists to preserve Jewish racial purity, letting in even atheist Jews but placing great immigration barriers to anyone not of Jewish descent - it is possible to convert. The Jews don’t encourage this and don’t proselytize, but it does happen.
Presumably, then, a convert Jew gets “in on the deal” with God, and thus can dump Jesus.
So, what if for some reason (something in the water, who knows) everybody decides to convert to Judaism? Seriously, one could simply look at both religions and decide which one is less of a hassle, and one might well decide Judaism is. If everyone so essays the matter, what does that imply for Christianity?