I am not so sure why I have to specify a group for the animated vector as target. It seem very redudant since the object animator that is used already has a path from and a path to. Therefore, shouldn't the object animator already know how to transform the vector drawable? If so why do I still have to set the group name as target?
A VectorDrawable can contain multiple paths and groups and an Animated Vector Drawable can use multiple Object Animators simultaneously to animate different parts of one VectorDrawable.
Specifying which part of the VectorDrawable you want to target with each animator is necessary to allow this sort of flexibility and scope.
For many types of attribute you would animate, think colour change or rotation, it may be impossible to guess which part of the VectorDrawable you intended to change unless you explicitly specified it.
You may say that if you are animating the pathData it should be obvious which part you are trying to change, but it doesn't really seem worth it for the Android team to try to engineer a solution to detect this when it's really an exception, better to keep it consistent.
Also there's absolutely no reason why you couldn't have a VectorDrawable with multiple lines drawn with exactly the same pathData(to look like just one line) which are then all animated separately to produce a particular effect. In this case you'd need to specify the different targets, so even with pathData you can't always infer what the intended target is.