When Lin An heard that Professor Cao's time was near, his first thought was of the Sorcerer's Sanctuary's headquarters space.
That space, supported by witchcraft, was sufficient to carry every soul longing for 'home,' 'final resting place,' 'haven of the heart,' and 'shelter.'
But clearly, this was impossible.
Professor Cao would not harbor any emotional attachment to Lin An's home.
The situation where a soul continues to exist in the world, anchored to a space, is essentially the soul being passively guided and spellcast by the space, leveraging the inert spiritual energy of the Spirit Realm.
The maintenance of the spellcasting effect is the sense of belonging to the space in the soul.
With a sense of belonging, the soul remains existing within that space. Without it, the soul loses the effect of passively casting this witchcraft, thus it cannot cling to that space.
