Because these sorts of speculations are empty and useless, given the paucity of the evidence.
We very often can find the truth. But what we do is to reject unsupported claims until there is enough evidence to give a proper evaluation.
So far, we may reject claims that there are ghosts. Given what we know, we may conclude that they don't exist. If new evidence supports their existence, we may revisit the issue.
You are damaging your credibility. Atheists are unique individuals. You weren't just any atheist, you were you.
I completely believe that it might not have made sense for you to be an atheist, or that you couldn't make sense out of life as an atheist, but that doesn't apply to any other atheists. You make the classic error of assuming that we are just like how you were.
eudaimonia,
Mark