They helped — Either because they thought the right of the crown was his: or to secure and advance their own interest. It seems God left them to themselves, to correct them for former miscarriages, with a rod of their own making.
Related Commentaries of 1 Kings 1:7
1 Kings 1:7
7 And he conferred with Joab the son of Zeruiah, and with Abiathar the priest: and they following Adonijah helped him.