Nothing, but they don’t make enough. Unless it claims to be 100% Vermont it’s likely blended with Canadian or entirely Canadian maple syrup.

Scarcity is not really the problem—it is price competitiveness. Many, possibly most, maple syrup producers in New England do not sell to national grocery store chains. You go to the sugar house and buy a jug which is typically much more expensive than what you’d find in a grocery store. But you also have more choices, since you can buy from a person who sells different grades. I rarely see more than one grade for sale in a US grocery store. I don’t mind paying a little extra for something I use in such small quantities to support a neighbor.