They’re not even the same currency at all, yet Steam or any other digital storefront decides to price a 80€ ($91) game the same as a $80 (69€) one when the conversions in reality are different to what the algorithm suggests. It’s reflected on Steam DB that Euro has a higher markup in comparison to US Dollar because of this, since I hear EU players nagging about paying 80€ at launch the same as US players don’t like paying $80.
It’s because one of the basic ideas of free market capitalism, that competition between suppliers will drive down prices to the lowest sustainable point, is a lie.
Everyone selling anything aims to be a price taker. That is, rather than sell for the lowest price that keeps them afloat they sell for the highest price they can get.