Imagine you have 3 windows visible at the same time: a videogame rendering at the refresh rate of the display 144 Hz, a video player rendering frames at 30 Hz, and a text editor rendering blinking cursor at 2 Hz. Because the videogame wants to deliver frames at 144 Hz, the desktop compositor has to deliver the entire desktop at 144 Hz. Asking the video player and especially the text editor to also deliver frames at that frequency would be wasteful. Irrelevant for desktops with fast discrete GPUs, but directly translates to battery drain on laptops.
It cost nothing to not change the pixels when you didn't press a key, no matter whether you weren't pressing keys at 60Hz or you weren't pressing them at 144Hz.
Vast majority of titles use deferred rendering, and lighting is done off screen too. Usually the only thing done to the "screen buffer" is a final post-process pass or a copy.
This is called 'compositing' but its similar in name only. It's a fairly efficient process where each color pixel is produced by reading these buffer targets and producing a final color in a shader.
This is entirely different from what composited apps do, where they build up the app's background into a texture, and push that onto the screen, with potentially multiple screen's worth of windows living in memory. This would be equivalent in video game terms to rendering every character and object in the level as 'stickers' and then making the final image of these cutouts, which would consume tons of RAM uselessly, and would force us to render crazy amounts of detail that would never get shown.
Regardless, video games normally update the entire screen (or window) every frame, because the screen is so dynamic. This is unlike Microsoft Excel which has a mostly static screen. Building Excel as if it's a video game is going to waste resources.