Why are there so many white tigers in captivity?

White tigers aren't a separate species, they're simply a rare version of the bengal tiger. In the wild, being white is a big disadvantage. As cubs they're more easily spotted by anything that might think of a tiger cub as being a nice snack. As adults, hunting gets more difficult because they're more easily spotted by their prey. In captivity they're protected from predators as cubs, and they're fed by keepers. So more of them survive. Also, us humans like the way they look, which draws visitors to zoos, so zoos are eager to get them.

Tigers are often bred specially for the purpose of creating white tigers.