Why are some tigers white?

It is a mutation. There are also white bison, elephants and gorillas. I don't think white tigers are actually albinos. The ones I remember seeing had blue eyes. The eyes of albinos are pink. The white tiger simply lacks the genes for yellow fur. Tigers ambush prey by hiding in long grass and pouncing on the prey after it has walked past. They have yellow fur to match the color of dried grass. A white tiger would be more conspicuous and would have a harder time catching prey. This is why most tigers are not white.