Why do you think non believers celebrate Easter and Christmas when you know full well they don't believe in Jesus or the whole Christian thing?
I believe it's because of tradition. People do what their grandparents/parents did.
Mostly they see Easter as the coming of spring and not a religious Holiday. Even if they go to church it's because of tradition.
Christmas--Who wouldn't want to participate unless you are of another religion? You get presents and parties, etc. There is no participation based on what Jesus did for them. They send X-mas cards.
Pray for their eyes to be opened to the true meaning.