When I did the Keys to the Kingdom Tour, one of the things they told us was Splash Mountain was considered a pool. Therefore, they were required to drain and clean it annually. Plus it has to be inspected by the county health department before it could reopen. It had to be drained and completely closed for no less than 30 days. People also keep bringing up Kali but Animal Kingdom is in a completely different county and thus subject to different local rules. Splash is in Osceola and Kali in Orange Co.
Splash Mountain's ride area and backup tank hold close to 2 million gallons of water and the ride itself is like 9 acres. A lot to drain and clean. Most of the parts for it to are custom made in Europe so if they encounter something unexpected, a new part could take awhile. From what they told us, a lot goes into getting it refurbished and approved in order to keep it running each year. As much as I would agree Disney tries to save money, I don't think they shut this down every year as a cost cutter. I'm sure more money is put into the ride for refurbishment than it would cost them in labor costs for employees to run it. It's a huge area to clean, repaint etc. They reuse all the water and it is pumped into huge holding tanks behind it when they need to drain it so no money is lost there. I think they simply choose Jan/Feb to refurb because its colder. It's not a money issue, it's county law.