There are many reasons why you might not want this feature enabled. Animation syncing is hard on the network - especially for players joining into the world. A well engineered animator should be able to sync itself up over time based on the controller inputs. For other cases, synchronization may not be necessary at all if the animations are non-critical.

Furthermore, there are a number of uses for animators that are purely logical. Random crossfades triggered by the network absolutely destroy this logic. For these logical animators, it may be perfectly valid to have the animator in one state for one player, but in another for another player.

I would like to see a checkbox added to the VRC_ObjectSync component similar to the Synchronize Physics box called Synchronize Animation that allows you to toggle the animation sync behavior.