I think what is being missed here is that most Americans will easily have their normal dietary needs met by most of the products sold in supermarkets. These are just special sections that cater for a few specific items that people probably miss. In the same way that someone from the UK might miss Marmite in the US (no idea if that is sold there or not). My BIL is a store manager and he said it's frequently based on requests. If enough demand is made then they stock them (his store is near a US army base in the UK) Anyone with an ounce of sense will realise that it's not that this is all that American's eat but that some of these are uniquely American or brands that American's really like. Also, the Baking Soda thing - we call it Bicarb so pity the American trying to find Baking Soda if they have no idea.

Some of the items in the American section are just stereotypes and not really enjoyed by many people. Only one of them felt like an "American Section" which was actually curated by an American.

it was my first guess too but I'm curious

That's exactly what I thought

No-one butters the cucumbers... It's buttered bread with cucumber slices in between, though as QBFT said it's a cliche and other sandwiches are far more popular. Also it is inside the slices bread. You do get open sandwiches but you still don't butter the ingredients.