What caused the extiction of the white tigers?

White tigers are not yet extinct. White tigers are also known as snow tigers. But no, they are not yet extinct, even.

The white tigers are merely color variations of the Bengal tiger, extremely rare in the wild. They are not a different species from the Bengal, and white cubs can be born at any time in a litter of normal colored cubs.

Also, the "snow" tiger is the Siberian tiger, not white Bengals.