that is because their messengers came to them with clear explanations but they said are human beings going to guide us? so they disbelieved and turned away. but god is in no need. god is independent and praiseworthy.
ذلك بأنه كانت تأتيهم رسلهم بالبينات فقالوا أبشر يهدوننا فكفروا وتولوا واستغنى الله والله غني حميد