Part of the reason is that this is a macOS browser. macOS's window management is a joke. But I think I'd use the tab tiling on Linux too, I do a lot of work with tiled browser windows and it's great, but also sucks when you want to have a window very small horizontally and the browser's UI gets squished along with any extension menus you're trying to use. Arc doesn't have that problem, you always have access to the full UI.