Why is the white tiger almost extinct?

The white tiger isn't recognized as a separate species.

It's the same ol' tiger, but with ONE mutation changing its colour scheme. The mutation is rare enough as it is, and then the poorer camouflage makes it a lot harder for those individuals to reach adulthood, making it rarer still.

White tigers have ALWAYS been rare, but there's been SOME every now and then. It's the result of a natural mutation, remember? But with the overall number of tigers dropping, a rare event becomes rarer.

Almost all white tigers in captivity are related to a wild-caught white male that was bred with one of his white daughters, which makes them prone to poor health due to the close inbreeding.