Manhattan is laden with manhole covers made in India. The only rationale I can think of is, it must have cost nothing to ship as they were probably desired for balast. That's the reason, incidentally, why there are slate roofs in Richmond, Virginia (it was used as ballast on ships from the Northeast). Or so I've been told.
Regarding the manhole covers, most Americans have no idea that we have nearly completely lost our metal casting industry. The ones that remain are either small scale niche shops, conglomerate companies that have most of their casting resources overseas, or are targeting aerospace or transportation applications. It has nothing at all to do with ship ballast-- only money, I am afraid.
Some have posted that a drive for increasing margins has pushed production overseas. In my experience, it has been a necessity to maintain margins— not increase them. At my company, we try to maintain an average margin near 30%.
Our customer then sells to consumers like you and me at a 40-50% margin, but at the maximum retail price we (i.e. consumers) will accept. We import 40-60% of our products and still have to skimp on historically typical durability and robustness to meet opening price point targets.