Plenty of Christians did spread the Gospel - it took over much of the world!
But perhaps many Jews knew - and still recognize - that what they know through their own original and ancient teachings is equal and sufficient, or even superior, for THEM.
Maybe all Jesus was doing in the first place was uncovering for them the depths of what they already possessed; and they felt or feel no need to change formally - under which perspective they may find efforts to convince them to change offensive.
(If Jews want to know about Jesus, they will come to Him of their own accord. Trying to browbeat Jews in threads like this seems no different to me than all the Catholic v. whatever-Protestant-flavor threads that we see on FR - big waste of time, productive of nothing but bad blood between people.)