Animals that are dieing from natural causes are few. They might have diseases that can not be cured so why waste the hard earned money that people are earning. We should be concentrating on the animals that we have caused to be endangered like the koalas. They have a reason the be protected.
A given species, plant or animal could be the source of a new medicine in the future. Or they could play a significant ecological role somewhere in the world that could effect things like crop yields and the climate. We need to preserve as many species as we can, because we don't know how doing so might help us in the future.