I'm going to offer a different explanation for why some hospitals are
haunted, since I would think that a ghost would want to go back to the
place where they lived or stay around their family. Since Recurrent
Spontaneous Psychokinesis (RSPK) is caused by someone who's in physical
or emotional pain, and there are a lot of people in hospitals who are
in pain, hospitals could be haunted not by the dead but by the living.
This could be especially true in mental hospitals where people's
perceptions of reality are warped. In fact, I think this is something
that should be looked into. A lot of patients in mental hospitals who
are seeing things may really be seeing something (and of course some of
the things they're seeing are still imaginary). They could be seeing
poltergeist activity, either created by themselves or by other people
in the hospital. As we said earlier in the entry about the different
types of hauntings, it IS possible in a poltergeist case to see
apparitions, but what's actually happening is the person is
telepathically projecting their fears to other people in the vicinity.
It can be witnessed by multiple people at the same time, but the
poltergeist agent has to be somewhere in the vicinity. No activity is
experienced while they are away.

Then for the abandoned
hospitals where there are no people anymore, they could be haunted
because the patients were mistreated or it could be residual from all
the people who were in pain when they stayed there. It's also possible
that the person "wasn't all there" when they were alive, and that could
be another reason why they're still hanging around.