I have the feeling that Disney would like to avoid the problem (i.e. cost) of patrolling and maintaining a large network of footpaths and bridges. As much as people would enjoy a casual hike or jog around the lagoon and between all the parks and hotels, it wouldn't exactly lead to revenue enhancement. Unless they position beer carts every 100 yards ... but dedicated walkers and runners are not exactly the beer-drinking, souvenir-buying types ... more like "frugal and fitness conscious".
The entire greater Orlando area seems to be anti-pedestrian by design. Did you ever try to use online maps to find a resort so close to an attraction that you could walk to it, only to zoom in and find that there are no sidewalks, crosswalks or pedestrian traffic signals? The authorities would prefer that you stay inside your nice, safe vehicle and do your walking only inside the theme park or mall. With wallet in hand.