Sforno on Leviticus 23:28/ספורנו על ויקרא כ״ג:כ״ח

1seeing that most of the people guilty of not practicing self denial do not do so to annoy G’d, but because they cannot resist the allure of the gratification beckoning to them, whereas most of the people violating the commandment not to work on the day do so because they want to indicate their independence of G’d’s dictates, the penalty of karet is in store for eating or drinking on the day of Atonement, whereas destruction of one’s soul is in store for people deliberately violating the work prohibition applicable on this day.