It's a logistical nightmare. You would have to have a bus making a "resort" loop, going to each of the resorts. How many resorts does Disney have? 15? Think how long it would take to get to the 8th resort on the run. By that time you could have taken a bus to a park and transferred to that resort's bus.
If you say there should be more buses and shorter routes, then it becomes too expensive. For example, say Disney ran three resort buses runs from the All-Stars. One ran to CR, WL, FW, Poly,and GF. The second ran to Swan, Dolphin, BWI, BC, YC, and CBR. The third ran to POP, SSR, POR and POFQ. Now you have tripled your costs and reduced the number of people in each bus (since it is going to 2/3 fewer resorts than with just one bus route). Now you have buses with only 10 people on them. Plus, each resort would need three bus routes. Otherwise, a guest at the Swan would have to transfer somewhere to get to the Poly.
Now factor in the fact that most people eat at the restaurants at their resort or at the parks. While many of us love going to the different resort restaurants, in reality there probably are not enough people to justify this expense.