Not So Simple.

The ancestor of Litori asked for his secret and gave numerous reasons for it. She was even willing to pay for it, but he refused.

Soverick was sure that her request was a cover for something, which she denied. Then she came with another set of people, and they forced him to either swear that he didn't know the secret to becoming a world god without a Supreme Law or prepare to be hunted by the Supreme Beasts. 

He didn't swear it so they confirmed that he had the secret. It was all they needed to know that they were not going to bark up the wrong tree or go on a wild goose chase by trying to use violence to get the secret from him. 

A single entity using violence against an immortal would be a bad idea. But a superconglomerate like the Supreme Alliance using violence to get what they want is a very efficient idea. Especially since they are so good at discovering the weaknesses of others and capturing them.