See, here's the thing on ghosts. When people are conceived, a new soul is created unless an old soul inhabits the newly formed structure. That's where you get people referring to people who are "new" souls and "old" souls. There are currently more people on the planet than have ever lived in history, which is why we are still creating new souls. Now as we get more crowded, there will eventually be a balance between people born and people dying (right now about 136 million born and 56 million die every year) and no more new souls will be created unless we move off onto other planets, but then there is the concern that the souls here won't be able to make their way to those new planets and so you will still have an equilibrium here and no new souls, only new souls on those planets.
However, when a great die off occurs, there is a space of time where there simply aren't enough bodies for all the souls, and that is where you have ghosts. That is why we have tales through history of them, but none for the non-believers to see today. So wait for a mass killing in the hundreds of millions, and then you should have them around for a year or two, enough for some people to notice them.
There you go, all explained for you as to why they exist and why most people alive today have never seen one.