Price was better and they had pet friendly cabins. Read about it here and see the pictures.
Cabins are worth it once you realize they're adding a bunch of fees.
Reservation Fee- This is the company selling you the cabin.
Cleaning Fee - They hire a 3rd party company to clean it after you leave.
Pet Fee - Extra to clean the place for pets.
Tax - Standard no matter where you stay.
The cabin in Cosby didn't have a reservation fee, only the cleaning, pet, and tax. The drive from Cosby to the Dollywood area wasn't that bad, even though it took 30 minutes. We used Google maps on my iphone and ended up taking back roads, which took us right to Patriot Park and the 50 cent bus ride.
If the cabins in the Gatlinburg area are sold out, or they don't have any pet friendly, then consider Cosby.