This is yet another cultural phenomenon providing evidence of the reality of spirit phenomena, and the inner fear that awareness generates, and for good reason. People have a long, troubled history with spirit encounters and forces of darkness causing great harm to them, and has happened again and again all through the ages. Because they are invisible, they do their work in an insidious fashion, and this can create many problems, particularly among disbelievers who will doubt those who can see such things and will begin to mock them and attempt to discredit them. Such campaigns have alternated with an overbelief in the power of Satan and the darkness, and people have mounted witch hunts killing many innocent people, as well as victims of spirit possession, who were believed to be witches but merely exhibiting signs of spirit possession to make them a target.
There are spirit portals, and these represent a danger to the living because the movement of spirits among dimensions is facilitated by a network of such energetic portals, and being in their proximity will guarantee encounters with such beings and, depending on personal vulnerability, will cause much trouble because spirits emerging from such portals are in search of a human target to possess for obtaining their energy to survive, so this is a deadly business for the dark spirits to find and attach to a human victim. So the association of cracks representing spirit portals is a naïve assumption, especially because cracks underfoot vastly outnumber spirit portals, but there is certainly a valid reason to seek a defense from existing spirit portals and the problems they can bring for humans in the vicinity. What is needed is a divine intervention, as through the Lightworker Healing Protocol, to relocate spirit portals to a safe distance from the vicinity of physical beings.