There's a standard for both "enriched macaroni product" and just "macaroni product." I don't believe anything requires you to choose the enriched one, other than the fact that doing any enrichment kicks you over to the "enriched" standard and you're then locked into at least a list of several mandatory enrichments.

Some states have laws requiring enrichment of flour, bread, pasta, etc. though, and that I think is what's happening with even importers opting for enrichment: it's necessary to have access to a nationwide market.