Lucian is one of the most fortunate of ancient writers, since more than 80 of his works survive. He's not alone there - we have a large library of Cicero's work as well.
But Cicero was considered a "virtuous pagan" by the church. This is someone who was never introduced to Christianity but was still considered to live a virtuous life. So they preserved his works.
On the other hand, Christians loved purging works they deemed sinful (how times have changed). And Lucian satirized Christianity, wrote about prostitues, and did plenty more they would have found distasteful.
But somehow, his work was so beloved in the Byzantine empire that it became part of the school curriculum. That's why we have so much of it today.
