User blog comment:DiegoAnime3000/RWBY Volume 3 Opening Scene is complete/@comment-25405817-20150612142856/@comment-10380701-20150612143818

The better question is why not?

Inititally, people thought This Will be the Day is still gonna be Volume 2's intro. That was quickly proven wrong once they released it.

So if this trend continues, every Volume will have their own intro.