Because his appetite is never satisfied, he cannot escape with his treasure.
The instances here given of the miserable condition of the wicked man in this world are expressed with great fulness and fluency of language, and the same thing returned to again and repeated in other words. Let us therefore reduce the particulars to their proper heads, and observe, I. What his wickedness is for which he is punished. 1.
Commenting on Job 20:10-22
Surely he shall not feel quietness in his belly,.... Or happiness in his children, so some in Bar Tzemach; rather shall have no satisfaction in his substance; though his belly is filled with hid treasure, it shall give him no contentment; he shall be a stranger to that divine art, but ever have a restless craving after more, which is his sin; but rather punishment...
UMBREIT translates, "His inward parts know no rest" from desires. his belly--that is, peace inwardly. not save--literally, "not escape with that which," &c., alluding to Job's having been stripped of his all.