The power of Saxon kings was never absolute, nor could it be safeguarded by military strength.  It depended upon the fulfilment of an unwritten social contract between ruler and ruled.  It was not enough for a king to be a respected leader in war; he had also to “be a good lord” to his subjects.  This entailed constant demonstrations of justice, reliability, accessability, and speed to reward good and faithful service and punish wrongdoers.  If, over the years, he showed that he lacked any of these qualities,the king and his heirs could be ousted and replaced by a new dynasty claiming kingship to the ancient ruling house.
    The king, while very powerful, required the ongoing support of his subjects, and the Kingship of Wessex was open to any representative of any line which could claim descent from Cerdic.  Kings were regularily replaced by relatives of an ancient ruler.  Consider the rulers of Wessex from Cerdic to Alfred the Great as reconstructed from the Anglo-Saxon Chronicle: