Why not moral anti-realism?

In honor of Rabbi Michi,
I really like your division between halakha and morality. These are two completely different fields, and in any case all the questions about “morality in halakha” fall away. But it seems to me that your belief in objective morality creates a serious problem: you are forced to assume the existence of two systems that originate from God and that for some reason sometimes conflict without a principled way to decide between them (you wrote that halakha will prevail in most cases, but it seems to me that you also have no clear procedure). So… why not moral anti-realism? The advantage is clear: you don’t have to say that God’s command is incompatible with God’s will and you don’t need any procedure to decide in the event of a conflict. There are no “moral facts,” and halakha expresses religious values ​​(and if I were a Torah keeper, I would try to formulate something along Hobbesian lines, contractarianism). Another advantage is that you don’t have to insist on the motivation to be moral as a “first rational being” or an axiom; morality is a rational matter, and the question “Why should I be rational?” She is tasteless.
So why the insistence on objective morality?