Your typical semi-religious or non-religious  Jew cannot relate to being a Christian. To them that that term synonymous with being a gentile - something very different. So tarring all Jewish believers as Christians (meaning Gentiles) is a rather transparent attempt by hostile forces to this movement to thwart their attempts at evangelizing Jews.
That, more than anything related to accuracy or theology is why these forces INSIST that Messianic Jews be called Christians...