Steam just doesn't support payment methods with high commission, like Pay Safe Card, which takes up to 24%. Regular payment methods don't add extra cost to games on EGS. FYI mobile payment also adds price to steam games, but you'll see it only after checkout.
Also, interesting info regarding games not being cheaper on EGS, while having lower cut from the store. Steam contract demand publishers to sell games with the same price on other stores. Steam also demands publishers to have a discount if a game was discounted on another store. (Speaking of "competition")
Are you a developer yourself or do you have sources for this?
If Steam contract demand publishers to sell games with the same price on other stores, how do you explain that many games are cheaper on other stores like GMG and Humble? Or doesn't this count because these stores also sell Steam keys?
Also, games on EGS that aren't on Steam have the same price than other stores charging 30 percent as well. That's definitely not Valves fault.