Because those who can enter the Molten Furnace Realm are all exceptionally gifted geniuses, each with their own understanding of martial arts.
They enter the Molten Furnace Realm because they have cultivated the most suitable martial arts for themselves, and if you ask them to change their cultivation technique now, it would be like asking them to abandon their current martial arts cultivation and change to something else.
If you are a world-renowned expert in the Molten Furnace Realm, would you change your cultivation technique just because you suddenly obtained a so-called Emperor Divine Skill, altering your most powerful original skill?
That would require immense determination.
So, although the Three Divine Skills of the Human Emperor are strong, they aren't very attractive to experts in the Molten Furnace Realm, because they have already paved their own path.
Moreover, changing to another path is extremely difficult.
