And if they did that? Resort rates at WL would go up. Why? Because Disney could say that you can walk to MK from WL.
Seriously, it's not really a negligible distance. When you consider how many people complain about the distance from the food court to the Little Mermaid rooms at AoA, and that truly is negligible.....well, the majority of guests are going to fall into that category or close to it...those that don't want to walk further than they absolutely have to.
So, Disney doesn't build sidewalks everyplace they possibly can. Those sidewalks would have to be lit, they would have to be patrolled for 'critters'...I have to imagine that critter patrol in the WL area would be substantial with the watery areas.
With two types of transport available, I figure WL is well taken care of.