Spoiler The ML owns that place. He literally uses it to keep the MC there, and said something in the novel about how he wanted to keep the MC within his grasp. He could pay off the debt, but the debt was keeping him shackled. The novel also shows how twisted the ML is, but he does indulge in the MCs bratty behavior which he finds enduring and will also put him in his place if he starts crossing boundaries too much....
Spoiler
The ML owns that place. He literally uses it to keep the MC there, and said something in the novel about how he wanted to keep the MC within his grasp. He could pay off the debt, but the debt was keeping him shackled. The novel also shows how twisted the ML is, but he does indulge in the MCs bratty behavior which he finds enduring and will also put him in his place if he starts crossing boundaries too much....