I am not a front end developer. Can someone explain the benefit of these low level APIs in a web development context? Is the purpose to eventually have complet

I am not a front end developer. Can someone explain the benefit of these low level APIs in a web development context? Is the purpose to eventually have complete GUI toolkits with even the underlying window managers all contained in the browser window? Or is it primarily a performance thing, to get 2d and 3d client side animation? Or something else all together? Edit: Another possibility -- prettier widgets. I just wonder what need is addressed by making these low level APIs available. (again, not a front end developer, so relatively naive about the whole field, especially state-of-the-art)