Have lived in both eu and us.

Agree, but the challenge on tax is that it's not harmonized across municipalities. This means that stores that are across the street from each other may have identical prices/profit margin and a different net price to the consumer. This would lead to consumer preferences biased by physical location and have lots of other weird side effects. You can see this in areas that border state lines when the tax is appreciably different.

Step one is a harmonized tax rate, but that's easier said than done.