AnimationTracks don’t replicate either, because they are also instances. AnimationTrack is an object that controls the playback of animations. It can only be “created” from LoadAnimation of a Humanoid or an AnimationController, but that doesn’t mean it still doesn’t follow standard replication patterns.
The only thing that replicates is the movement applied from the AnimationTrack to any relevant Motor6Ds. The client network owns their character and thus the movements they apply replicate. This isn’t an exception for animations, since animations are movements of CFrames.
Also see: Pose | Documentation - Roblox Creator Hub (substantiation for the second paragraph)