Albert Barnes Commentary 1 Chronicles 1:29

"These are their generations: the first-born of Ishmael, Nebaioth; then Kedar, and Adbeel, and Mibsam," — 1 Chronicles 1:29 (ASV)

These are their generations - As Shem was discussed after Japheth and Ham (1 Chronicles 1:5–16) because the genealogy was to be continued through him (see Genesis 10:2 note), so Isaac is now discussed after the other lines of descent from Abraham have been completed. The same principle gives the descendants of Esau priority over those of Jacob (1 Chronicles 1:35–51; 1 Chronicles 2:1).