The oath became a signal that indicates a person's speech is not reliable because the modern world have announced that the truth lies with mankind, and mankind can have access to the truth so that the oath is not required.
Swearing has become a sign to show that the words were not reliable because the modern world has announced. Truth with man, and a three-car access to the truth. So there's no need to swear
The vow is become the signal that the words of the man is unreliable because the modern world has announced that the truth with human and A human can reach the truth. So the vow is not necessary.