A lower price may attract more buyers, leading to more money overall (rather than only seeking to maximize each individual sale)
And which platform has the most potential buyers, by a long shot? Steam. That’s why you’re usually seeing all time lows on the Steam platform, because the sheer amount of buyers outweighs the per sale loss.
If a dev wants to make X per game, they could get X with a lower price point on Epic. To still get X, they could sell the game for a lower price on Epic. That lower price may get some people to buy the game who wouldn’t buy it for anything more.
The game can still be sold on both Steam and Epic, which is the whole point of this discussion, so Steam having a larger userbase is irrelevant.
If the userbase is irrelevant then X per game is also irrelevant. X per game matters only in the context of how many sales you’ll make. There’s a strong correlation between sales and userbase because more users means more potential sales.