I sent plagues among you like I did Egypt. I have slain your young men with the sword, And have carried away your horses; And I filled your nostrils with the stench of your camp Yet you haven't returned to me," says Yahweh.
"Yet have ye not returned unto me, saith Jehovah ..." This dire lament is dramatically repeated five times (Amos 4:6,8,9,10,12), somewhat like a refrain.  It has the utility of constant emphasis upon the truth that the disasters were not mere punishments, but solicitations for the chosen people to repent and return to the Lord, the purpose of the Father being benign throughout.