Usage of も at the end of a sentence?

I found this sentence in an anime: 人や物に化けられるが、実戦では役に立たないことも。

From what I understand, it means: They can transform into people or objects, but it is useless in actual combat.

But I don't quite understand why it ends with も instead of just ending with こと.

Does anyone know why or have resources that explain this?