The workflow in game engines is often tuned for extreme flexibility, reusability and fast iterations.
E.g. there is usually a predefined set of animations that are blended, layered and reused like crazy. If needed, those animations are combined with inverse kinematics to increase the believability. With those setups, you can basically tell a character to walk from A to B and it will automatically have the animation. If you don’t like the path, you can modify it. If it is still not enough, you can steer the character directly and record the movement.
I don’t know about other 3d modelling software, but in Blender, it can be very tedious to set things up and I always think twice whether I really want do duplicate a character for a quick test, because it is not as simple as that due to the way Blender works. In any game engine I have used, you just copy the character, swap the logic that controls it and then it works.
I can imagine that if someone has to create a cartoon with several episodes, it can be more efficient to use a game engine due to their workflows.