Frankly
It was far more complex than Ryu could have imagined, it was no wonder that he hadn't understood what had happened previously, but now that he was piecing things together, it was slowly beginning to make more and more sense.
The changes in the Realm Heart began from the moment his Beyond Perfect Extreme Spiritual Foundation had appeared. What was key here, though, was that the appearance of the Realm Heart, or more accurately, the method by which it was connected with Ryu was very similar to his Spiritual Foundation.
The Realm Heart, too, was an existence within the Abyssal Plane. It, too, was an immature sort of construct that had to be slowly evolved and molded into the future. And most importantly, when Ryu had been a "cripple" in his second life, it was the Realm Heart that had replaced the function of his Spiritual Foundation and allowed him to continue cultivating as though nothing at all had happened.