Because test frogs didn't die they were released into the wild.

Pregnancy test helped to bring frog-killing fungus to the US

When improved pregnancy tests were developed in the 1960s, the advance came with an unexpected side effect: a role in the spread of chytridiomycosis, a lethal fungal disease that has wiped out hundreds of species of frogs.


Humans are responsible for the disease’s spread in North America, by introducing an invasive species that acts as a carrier—unusually, Xenopus frogs do not die after contracting the disease. “If it were a natural spread, a conservation biologist might say maybe we should do nothing. But this really says we need to not let nature take its course,” says Vredenburg.

Amphibians wiped out before they are discovered
Fungal disease drives the loss of 30 species in Panama.
Amphibians are the oldest class of existing four-legged vertebrates, having been around for 300 million years. "Part of what's so alarming is that these long-term survivors are dropping off the face of the Earth right now," says Vredenburg.
[link to www.nature.com]