Why is there so much incest in Game of Thrones?

Why is there so much incest in Game of Thrones? In the A Song of Ice and Fire novels, the Targaryens continued to incestuously marry brother to sister “to keep the bloodlines pure” as had their ancestors in the Valyrian Freehold. For a time, at least, they also continued to practice polygamous marriages.

In the A Song of Ice and Fire novels, the Targaryens continued to incestuously marry brother to sister “to keep the bloodlines pure” as had their ancestors in the Valyrian Freehold. For a time, at least, they also continued to practice polygamous marriages.