Because regardless of the state of the animation, the ride eats people better than any other ride in the park, and is an essential for crowd control. Being virtually the only big thing in the back of the park, it's definitely "do-or-die" when it comes to keeping it operational.
Whats even funnier about River Adventure is the amount of budget it gets, and the amount of attention it gets, yet it still is never up to par. Ever wonder why rides like Ripsaw go down for its annual only to come back looking nearly the same as it did two weeks prior? Where do you think its funding gets thrown to? I'll be the first to admit that keeping something running like its brand new 10 years later is quite a feat, but for a ride where animation basically is the experience... accompanied with a big fall at the end, you'd think there would be a little more emphasis placed into the show element...