Well, because when one is making up arbitrary things, they might as well be remotely interesting, and based on my whims.
Seriously though, that it is teeming with life is the *one* thing that sets Earth apart from the other planets we know so far. That's kind of the whole big deal about it. If this criterion doesn't matter, then why care about "Earth-like" at all? What about the Jupiter-like and Neptune-like and Venus-like planets being discovered all the time?
Oh wait, that would be silly, because we already know the universe is incredibly big, and just about anything we just define by size, orbit and mass is going to exist in abundance, including round things roughly the size of Earth.