Let's say you walk between BWV and Epcot in the morning (approx 10-15 min each way) and BWV and MGM in the evening (approx 15-20 min each way.) That's easily an hour per day of largely non-productive locomotion. (Non-productive as in it doesn't directly impact your ability to get to any attractions, restaurants or other worthwhile destination.)
Is there a lot of walking at WDW? Of course. But why pile on another hour of unnecessary exertion. Yes, there is the "stop and smell the roses" factor, but after a week of doing it with 70 pounds of toddler on the front of the stroller, it gets old. I much prefer the 2 min walk to a bus stop followed by 15 sitting on my butt. And, frankly, the kids think a bus ride is just as much fun as any other mode of transportation--they don't immediately wrinkle their noses as many adults do.
I'm sure there are many who prefer to walk, and I completely understand that. There are times I do prefer to walk. But as long as our children are stroller-aged, folding that stroller and climbing onto a bus is preferrable to the alternative workout.
To each their own...