I guess for us, the following reasons are key:
1. Theme - The 19th century NW United States theme is a favorite of ours. We actually stayed at Glacier Park Lodge this summer and it was amazing how similar the two resorts are in theme (WL is much nicer, however

) Disney really did a great job with this resort.
2. Pool - We've always enjoyed this pool most of all. I'm not sure if we just hit it at convenient times or what, but it always seems like there is plenty of room.
3. Location - It is nice to be somewhat secluded from the parks...when we've stayed at some of the other resorts, we've often felt like we went from a theme park back to a theme park to sleep. Wilderness Lodge is definitely not like that at all.
4. Design - The design of the lodge makes it easy to get anywhere in the lodge. Some of the other resorts are very spread out. It is great to be able to stay inside to journey to the Roaring Forks to refill your mugs.
5. Transportation - We've always had a great experience with the transportation, and it is nice to be able to take the boat to the MK.
We love WL, and if you stay there, I hope you do too!