They don't need dark patterns, they're already making a boatload of money indeed. If the trend continues, that means more paid consultants working on open source Linux desktop libraries [1]. Win-win in my book.

It actually feels good that the 30% cut Steam takes out of my purchases partly goes to improve my Linux desktop experience. Better for me as a user than if they were taking a smaller cut and focusing on Windows only.

1: Valve has been sponsoring work on Wine, Wayland, KDE, mesa gfx drivers, dxvk, and others.