Why do christians celebrate pagan holidays?

Jesus does tell us that men will follow the doctrines of men rather than the doctrines of God. Is this why christians celebrate Easter and Christmas? Both the holidays began as pagan celebrations of the spring solstice (easter) and the winter solstice ( christmas). Then christians added christian meaning to them so that pagans would be more willing to join the church. Celebrating these holidays was never commanded by God like remembering the Passover was so why do christains celebrate them and what reasoning makes it ok to celebrate them?