Because it has been a fact of life for the entirety of everyone living's life.
nCoV is a new threat that can kill, of course people will worry about it, it's instinctual.
We also don't have a vaccine for it yet, and an estimated 30% of infected people need hospital treatment, which is surely more than the usual flu, and requires more specialised & cautious care since less about it's known.
As the US' CDC says in the other nCoV post on the home page:
> The complete clinical picture with regard to COVID-19 is not fully understood.
It might just blow over and be fine, sure, but I don't think the response or caution surrounding it is irrational.