If life could spring up here (as they claim) from existing material merely by chance, then why shouldn't we assume that other life could spring up in other environments based on different materials?
In fact, if life arose here by mere chance, then it should also have arisen pretty much all over the universe... it should be everywhere.
I don't think NASA or anyone else interested in astronomy doubts life can exist under extremely different conditions than we are accustomed to on Earth.
Finding life thriving around thermal vents, with no sunlight, deep in the ocean on Earth opened many eyes.
For all we know, there is an awful lot of non-carbon based life out there.
As I posted earlier, astronomy is still in its infancy. Much more so for astrobiology.