True, but even if Steam were to offer a x% lower cut on sales for Linux users if the developer makes a Linux-native build, it’d still not entice many to build and maintain a native port if they are only saving x% off a tiny y% of users. Other poster’s point being that incentives like this would actually become enticing to companies when Linux market share (Proton users) increases.
Doubtful Steam is gonna offer a share cut on all sales when it runs on Proton for the 2% of userbase using Linux, and from that only a minority would care whether or not it’s native anyway.