A general expression (مجمل) gathers several elements under one description. A detailed expression (مفصل) unfolds them. This ordering may create anticipation followed by clarification.
“Amaddakum bimā taʿlamūn” introduces the blessings collectively. “Amaddakum bi-anʿāmin wa-banīn” then identifies prominent elements of that collective gift. The second sentence thus functions as an explication of the first.
The choice is whether to present the two clauses as parallel, equally independent reports or to let one spell out the other. In this passage the second relation is the significant one.