They don't. They realize that it's not Jesus' birthday and the traditions associated with the holiday have origins with other pagan beliefs. They do consider the DEATH of Jesus to be more important because of what Jesus' life and death accomplished
No Jehovah's Witnesses don't celebrate Christmas because Jesus never commanded his disciples to celebrate his birth. Jesus did command his disciples to preach throughout the world Matthew 24:14,28:18,19. Jesus also set the example for us to follow. Also because the ancient pagans would worship their sun god on the 25th, on top of that the first century Christians would not even celebrate birthdays do to their ancient pagan origins. Birthdays had a lot to do with magic, spiritism, superstition and astrology. I think Jesus would not condone his birthday being celebrated do to it's pagan origin. Jehovah's Witnesses always strive to follow the ways of the first century Christians and follow in Jesus Christ footsteps.
No, Witnesses don't celebrate Christmas. Not because we don't respect and love our Savior but because we do. If you you knew and understood the Biblical based reason Jehovah's Witnesses reject Christmas as an unacceptable observance from God's standpoint and not a man made tradition whose roots are steeped in falsehoods, well you wouldn't celebrate either. Please consider the Bible principle Jesus stated at Mark 7:9-13 showing what can result when men attempt to elevate tradition over Truth. And yes, Jehovah's Witnesses do engage in some celebrations. Thanks for asking.