Just like giant open world games load massive maps dynamically, couldn't we load separate maps, menus, and virtually any interface or 3D setting via that same dynamic loading method? Without changing the environment, it seem like interfaces and various locations within the game could all be loaded dynamically the same way massive open world maps are loaded as you walk through them. 

Why isnt this done? I see so many modern games where you have to wait a minute or more while the match / map / level is loading. I know there's a latency involved with connecting peers but that doesnt take more than a few moments in my experience. What issues exists with this concept to stop it from being used to eliminate loading time involved with loading map / level / interface data?