I have a question: of all the laws that God gave through Moses, people today claim that only the Ten Commandments are still valid - well, actually only nine of them, because the fourth commandment is either relegated to Sunday or else consigned to 'ceremonial laws' which are, according to them, on the scrap heap. Yet these same people will also claim that marriage is honourable and that homosexuality is condemned (neither of which is actually in the Ten, though marriage can be inferred). So why is it that only the Ten are considered still in vogue?
All good comments and thoughts, but there is no simple answer. Basically, only the 10 Commandments are "still in vogue" because Christianity sees them as the essence of "moral responsibility" taught by the Messiah. In the Messiah's "Sermon on the Mount" he specifically mentioned the prohibitions against murder and adultery and in Matthew 19:16-19 he specifically cites 5 of the ten and then explains a bit more in Matthew 22:34-40.
Also, Moses carried the two tablets with the 10 written on them, and when YHWH spoke to the people in Exodus 20:2-17, what He said has been equated to the "10 Commandments", mistaken as "the only commandments".
Christianity generally teaches that "only" the 10 commandments were handed down at Mt Sinai (Exodus 20:1-17) thus justifying their dismissal of all the others. But they are not the only commandments. In fact, ALL of YHWH's commands are contained within the ones that have been numbered 1-10 and named "The 10 Commandments."
In what is generally called commandment number 2, Exodus 20:3, "You are to have no other gods before me", the explanation actually goes on and in 20:6 YHWH explains "...but displaying grace to the thousandth generation of those who love me and obey my mitzvot." Thus, all YHWH's commandments are summarized right there as "love me and obey my mitzvot."
In fact Judaism does not generally call them "The 10 Commandments"; they are known instead as the "10 Words" or "10 Utterances" acknowledging that ALL YHWH's commands are summarized in them. The "10 Words" in ancient times were read and recited in the synagogues of the day because they were greatly revered - the Words actually spoken to the people directly from YHWH. But many Jews, like Christians, began to think they were the "only" commandments, so the practice of reading and reciting them in synagogues was largely abandoned.
It seems your observation is really about the lip-service people give to YHWH about who He is and what He asks of us. You pointed out that Christianity relegated His command to "keep the Sabbath and honor it" by changing their observance to Sunday and creating a "scrap heap" where they put other laws they don't care for, and embracing man's acceptance of homosexuality. The list could go on and on. Few obey "do not commit adultery" and "do not steal" and "honor your father and mother", etc.
Actually, as YHWH continued to teach His people for 40 years in the exodus, He would often tell the people "you are to be holy, for I am holy" (Leviticus 11:45 for example). So there need not be "10 Commandments" for ALL of YHWH's commands are in those two words: "be holy". We are holy when we obey YHWH and live our lives by the commandments He gave. We are not holy when we "pick and choose" which commandments we want to agree with and which we want to put on the scrap heap.