Because the outage didn't lead to the poisoning. Operator negligience and poor design did.

If I built a chlorine tank out of toothpicks and duct tape, and it leaks everywhere and kills people, you don't publish a headline that says DuctTape and Global Toothpicks Inc are responsible for chlorine deaths.

"A leads to B" means that A resulted in B. It doesn't imply that A was the root cause of B or deserves blame for B. For example, "heavy rainfall leads to flooding" can be true as a factual statement, even if the blame goes to poor drainage infrastructure. Also, the headline is in German and translates as "15 guests injured in Phantasialand".