Why does Matthew's Gospel trace the genealogy back to Abraham instead of Adam?

Les teaches that Matthew's Gospel opens by tracing the genealogy only back to Abraham, not to Adam. The reason is that Matthew presents Christ as the King. That whole concept of a coming King comes out of the Abrahamic Covenant, not out of something God promised to Adam, but what He promised to Abraham. Therefore Matthew's genealogy goes back only to Abraham because he is presenting the King, the One who will rule and reign not only over the nation of Israel but over the whole world. By contrast, Luke's genealogy goes all the way back to Adam because Luke presents Christ not as King but as the Son of Man, tying Him to Adam, the first man. Paul then refers to Christ as the second Adam.