Why doesn't the Grinch like christmas?

Theodor Geisel, who wrote under the pen name of "Dr. Suess," never gave a backstory regarding this famous yuletide creation. The book "How the Grinch Stole Christmas" was written and published in 1957. Geisel did say that the Grinch reminded him of himself as he attempted to rediscover something of the real meaning of Christmas, but this was never part of the story. In fact, the only reason given for the Grinch's hatred of Christmas is that his heart was "two sizes too small."

The Jim Carrey adaptation to film in 2000 of the Grinch made much more of a backstory to flesh out the plot of the film, but did so without any creative input from the author.