First, and at the risk of dabbling in gold-bug nuttery (I am not one), the paper spot price of any PM and the retail prices of physical bullion products shouldn’t affect your purchase decisions. Yes, you’ll pay a higher premium for an American Eagle, but you’ll sell it for a higher price. Generally, I think the only way to narrow your spread is with quantity, not product.
As to your question, I think it’s part psychological & cultural. We know and understand that coins are “money”, but bars are something more mundane and inanimate.
I further think that for whatever reason, as far a bullion goes, coins are just more popular, hence more expensive. So many infomercials shill mint-proof coins, coins used to be (maybe making a comeback?) a popular graduation, retirement, wedding, etc. present. You can buy fractional 1/2, 1/4, 1/10 coins of at least Eagles and Maples.
Also, insurance for home storage? Pretty much no homeowners/renters policy covers bullion (or cash for that matter) over a few hundred $$$. But (I can only speak for my insurance) I can purchase a VPP (valuable personal property) rider for about 1% / year of the value of the *coins*, but bars are apparently not insurable under any circumstances with my policy.
