Humans have only three places where they can develop a soul core, located at the center of the forehead, the chest, and the Dantian. By that time, to think of opening a third soul core amidst the chest, sandwiched between the two great Yin and Yang Complementing soul cores, was pure fantasy. It required first severing the original connection between the two big soul cores. If he did that, Huo Yuhao would have simply self-destructed.
In other words, if Huo Yuhao chose to develop his second soul core in the Dantian, then in the future, he would have no possibility of forming a third soul core. Even if he were powerful, he would not have the strength to become an Ultimate Douluo. In that case, he would not be able to inherit the godhood of the God of Emotions.