Why do most atheists profess to know Christ yet display a complete lack of

I've read a couple of your questions and they really don't come off as rational thinking.

I am neither an atheist nor a Christian, I'm a Jew.
I don't see atheists professing to know your religion’s redefined concept of messiah as the premise of your question claims.
Christians most often use “Judeo-Christian” to imply that Christianity is a logical successor from Judaism. Nothing could be further from the truth. Judaism has been complete and able to stand on its own as a viable faith for nearly four thousand years.
I have only seen it very rarely used by Jews and when it is used by Jews it is used for different purposes and different implied meaning. The few Jews who use it may claim they are trying to speak to shared values of both Christians and Jews. Jews also share values with ethical Hindus, Muslims, atheists, and people of many other religions. Jewish beliefs are just as different to Christianity as they are to Hindu belief and you don't see Judeo-Hindu as a phrase.
I also see some people using the phrase Judeo-Christian to refer to a God concept. For most Christians, their deity is a triune godhead with a dead Jewish man as a god in human form. An incarnate deity is a complete contradiction to the Jewish concept from the Hebrew Bible and what ALL Israel is recorded as hearing when they experienced their direct encounter with the Divine at Sinai. There is no "Judeo-Christian" or shared concept of God from the Tanakh to the New Testament. The phrase Judeo-Christian is illogical.
Leave Jews ( the Judeo-) out of your assumptions here please. In contrast to the Christian religion that often declares its adherents “separate from the world”, Judaism is a world-affirming faith that stresses the importance of personal accountability for behaviors and our path of Tikkun Olam ( repair and of the world to harmony, justice, mercy, compassion). The nature of God in the Tanakh is what the entire nation of Israel directly encountered at Sinai when they all affirmed God is ONE, an incorporeal Creator. Believing Jews believe that God did not lie to us when God said to all Israel at Sinai God does not become a man. Nothing is said that limits God's omnipotence to do anything, God simply told Israel to worship God to the exclusion of any and all other entities. Israel began doing this in a world where kings were seen as gods or incarnate manifestations of animal or celestial gods. Christianity obligates its adherents to worship an incarnate deity in complete violation of the core of the covenant of faith of Israel. God is never exclusive to Israel in the Torah. All humans are created by God, Jew and Gentile...all equal before God and merit equal judgement and blessing. Israel took on greater obligation to strive to honor the gift of life in living as a light unto the nations to restore the world to holiness; it is a world affirming faith. Humans are not born with a burden of sin, but with a blank slate having both a good inclination and an evil inclination and, as it says in Genesis, can master the evil inclination.
Contrast this with the New Testament replacement theology that has humans born in a state of sin that requires a one time, one size fits all human sacrifice to remove this "blot" of a sinful nature and appease their god to justify their existence. Contrast the nature of God who is one that becomes a man..(God incarnates into Jesus in the New Testament) to an incorporeal God who does not incarnate. This means Christian dogma rejected God’s commandments to Israel at Sinai and they are obligated to believe God lied to all Israel when he said God does not become a man. They are then also obligated to believe Malachi lied when he declared God said He does not change. Their New Testament teaches that only people who believe in Jesus and accept that his death was a sacrifice for sin and a sinful nature can merit God's blessings and that everyone else deserves eternal torture in their underworld hell ruled by a demon deity Devil who can battle God.
How can one say there is a “Judeo-Christian” anything when Christian dogma is foreign and antithetical and attempts to redefine or negate every part of Torah? As you can see we don't share worship of the same God despite their claims and attempts to tie their religion to Judaism. Torah obligates justice; there is no justice in the sacrifice of an innocent human. God forbade Moses from taking on the sins of Israel when he offered to do so. God told Moses no, every person is directly accountable for their own sin.

Atheists do not believe in any deity. Therefore, they do not profess to know the deity of Christianity.

I don't know Christ I know about the religion started around him.

I don't believe Jesus is the saviour and son of god. I don't claim to "know" him.