Is cost not reason enough? It costs 3 less than a Shrieker and a turn less than a Graboid, while being entirely in element.
Yes, it's harder to burrow and the burrowing isn't optional but, given that that effect is clearly passive, it could potential burrow with an ability.
The more worrying aspect is how the unupped compares with its dragon, being only 1 ATK lower for a lot less cost.