The same reasons why someone walks away from loving parents. Rebellion, disobedience, seeking an "easier" alternative, thinking "I know best", thinking themselves into knots ie "I shouldn't have been born into this family", "I don't fit in", "I can't live up to Dad and Mum's expectations" etc Often boils down to disbelief, and rarely ends well. The question being, "what am I running away from?" The happy sequel being that God waits, in grace, with hands outstretched to receive and bless those who return to Him in repentance.