Why have wildlife experts only estimated the number of endangered species in the world?
Wildlife experts believe that many species of plants and animals have not been discovered or studied yet, so the total number of endangered species can only be estimated.
This is the case because there are simply too many species, and it takes time to documents them; because some areas (ocean bottom for example) are very hard to access and because sometimes it's hard to know whether we're talking about a new species or a variation within the same species.
so if we even don't know how many species there are, it's even harder to know how many are endangered.
They can only estimate because- 1) they can't estimate how fast they can brood 2) they don't know if their predators will reproduce fast 3) they don't know if people will stop killing and destroying habitats 4) They don't know where all the species are, they might have escaped into other places fit for them to live