Why did Islam mandate freedom of belief regarding entering into it, but reject departing from it?

Islam does not command freedom of belief; rather, it commands belief in Allah, His Oneness, obedience to Him, obedience to His Messenger, and entering Islam entirely, as Allah Almighty says: "O you who have believed, enter into Islam completely." Whoever believes that it is permissible for anyone to practice a religion other than Islam is a disbeliever and must be killed if he does not repent. As for the saying "There is no compulsion in religion," it means that compulsion is not needed in religion because the truth is manifest, not that a person has the right to choose his religion after knowing Islam. The punishment for apostasy, which is death, is not applied to one who apostatized and concealed it, but rather to one who openly declared his apostasy. This is to protect the Muslim society and its entity. The openly declared apostate is treated as someone who has committed a crime of high treason that threatens the security and stability of society.