Ghosts werent exactly a common occurence,probably because they are usually a big problem to people who dont dwell on magic(and MC sucks hard on his spellcasting,even after he got better and more levelled),most of the locations that endured the war were sacred temples(which probably were warded to avoid having lost souls binded to them),Quetesh temple have seems a quite fair amount of death,and yet not even one soul got binded to the place(aside from MC mom)...Erevi tower too,saw a plenty share of souls lost before their time,and yet,not even one of them returned to haunt the place,and the same goes for the Forsaken temple that the orcs were using as base until they managed to annoy the shit out of Mc...
Opportunity to put ghosts werent lacking,so i think maybe the criter Tinkerer uses for them appearing is different from ours