אִם־יֶחֱטָ֨א אִ֤ישׁ לְאִישׁ֙ וּפִֽלְל֣וֹ אֱלֹהִ֔ים וְאִ֤ם לַֽיהוָה֙ יֶֽחֱטָא־אִ֔ישׁ מִ֖י יִתְפַּלֶּל־ל֑וֹ וְלֹ֤א יִשְׁמְעוּ֙ לְק֣וֹל אֲבִיהֶ֔ם כִּֽי־חָפֵ֥ץ יְהוָ֖ה לַהֲמִיתָֽם׃
If one man sin against another, God shall judge him; but if a man sin against the LORD, who shall entreat for him?’ But they hearkened not unto the voice of their father, because the LORD would slay them.
Akeidat Yitzchak
The reason that sins committed between different human beings are not subject to atonement of Yom Kippur is, that any sin in which man's body is the major party, can only be atoned for by that same body making the appropriate restitution. When reconciling oneself with one's fellow man, it is the senior person, the scholar, who must make the first move, just as Abraham had done with his nephew Lot. (Genesis chapter 13)