Why has Saint Christopher been de-sainted?

He was not de-sainted. He is still considered a saint, but since no historical data can be verified of his existence, his Feast Day was removed from the Roman Catholic calendar of saints in 1969. However, the Eastern Orthodox Church still honors St. Christopher's Feast Day on May 9.

Lots of people still venerate him and carry his medal as a protective charm. St. Christopher is considered the patron saint of travellers.