1. it’s not only in Vue, you can see the similar thing in React
2. it’s all about components
3. it’s not in clutter, components make it look more obvious that what the part of our app does, while directives could be mixed with your different tags, which is cluttered for me.
4. I believe there’re technical reasons too:

they are now only used for applying low-level direct DOM manipulations. In most cases, you should prefer using Components as the main code-reuse abstraction. — by evan