Also, we have a huge amount of mental architecture devoted to understanding and remembering spatial relationships of objects (for obvious evolutionary reasons). Using that as a metaphor for purely abstract things allows us to take advantage of that mental architecture to make other tasks easier.
A very structured version of this would be something like a memory palace where you assign ideas to specific locations in a place, but I think we are doing the same thing often when we talk about ideas in spatial relationships, and build loose mental models of them as existing in spatial relationship to one another (or at least I do).
Also, we have a huge amount of mental architecture devoted to understanding and remembering spatial relationships of objects (for obvious evolutionary reasons). Using that as a metaphor for purely abstract things allows us to take advantage of that mental architecture to make other tasks easier.
A very structured version of this would be something like a memory palace where you assign ideas to specific locations in a place, but I think we are doing the same thing often when we talk about ideas in spatial relationships, and build loose mental models of them as existing in spatial relationship to one another (or at least I do).