> i wonder why they haven't done the same on Windows
Probably because a lot of people feel like they need exclusive fullscreen for best performance and/or latency. But in reality borderless fullscreen is exactly the same when games use the DXGI flip model. It bypasses DWM (the compositor) to render directly to the display when only the game is visible and seamlessly allows you to switch to other windows. You can even disable Vsync and it will allow screen tearing when bypassing DWM.
I was playing Helldivers 2 in a small borderless window in the middle of my screen last week. I use fullscreen because it always works, except when switching apps, which I just don't do when I'm exclusively playing a game. Indie games seem to have the most trouble with borderless, with offsets, taskbar still visible, etc. It seems rare for an Indie game to not use fullscreen.
Probably because a lot of people feel like they need exclusive fullscreen for best performance and/or latency. But in reality borderless fullscreen is exactly the same when games use the DXGI flip model. It bypasses DWM (the compositor) to render directly to the display when only the game is visible and seamlessly allows you to switch to other windows. You can even disable Vsync and it will allow screen tearing when bypassing DWM.