Because this is far from the first evidence. There is plenty of evidence for liquid water on Mars both past and present. In fairness, the article mentions this.

Because this is far from the first evidence. There is plenty of evidence for liquid water on Mars both past and present. In fairness, the article mentions this. In spite of the headline, it only claims the first direct evidence. Personally, I think even that is a bit of an overstatement. To me, this is simply one more bit of evidence that supports the current scientific consensus.