"Jake, The Trader" 

Letting someone control your soul, even if the controller was someone close to you, would not be something pleasant. 

The feeling of one's own soul being held in other people's hands, regardless of whether the person was a close one or not, was nauseating. 

Even people who had been together for more than decades would not easily let the other party control them, much less a soul, which was the most important thing for all ability users. 

With a soul, they could still be revived or become spirits and embark on the journey to cultivate power as a spirit, which was like a second chance in life. 

However, without souls, one could not become spirits or reincarnate, and that means their life would end right there with no other possibilities. 

This was why, even though soul masters were unique, many ability users secretly hated soul masters.