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.
Part of it is that EU countries charge VAT on digital sales and prices must include it, while in the US there’s sales tax instead, which depends on the state and is only added at checkout time (and also often lower or even zero for digital goods). For example if I pay 80 Euro in Germany, then Steam gets to keep 67 because those 80 Euro include 19% VAT.
The other part is that in a market economy, prices are determined by what generates the most profit, and not necessarily related to cost or based on fairness. EU customers apparently pay 80 Euro often enough that it makes more money than 60 or 100 Euro so developers set their price to 80 Euro.