Likely because it’s very deadly, spreads rapidly, and now that the virus has transferred from birds -> cows -> humans, it could start to mutate into something that spreads human to human.

> Human infections with HPAI A(H5N1) virus have been reported in 23 countries since 1997, resulting in severe pneumonia and death in about 50% of cases.

https://www.cdc.gov/flu/avianflu/influenza-a-virus-subtypes....