It's a good question.
Based purely on a guess, I'd say that human antibodies are constructed in such a way that other parts of the immune system do not destroy them - in other words our natural antibodies pass a "self or non-self" test.
I don't know whether that applies to the immunoglobulins.
But I think bat antibodies might make us very sick
And now I see from the fresh links that bats don't have the same kind of immune system as humans. Antibodies are not made by bats.