I doubt that it's because Portland is a "pretty new" city; humans have been dying in this area for millennia. It could just be that ghosts aren't real and you're just full of shit.

I like this theory. There are places in Oregon with ghosts, for sure: The ghost towns to the east, some of the older coastal towns where residents were lost at sea, in the areas where the Umatilla were slaughtered after daring to stand up to the Whitmans. But Portland? Shit, Portland tears down most of the potentially scary stuff before it has a chance to weird people out. I'm sure Chinatown would have a lot more ghosts if the city didn't slowly bleed it out of existence (which was still preferable to what it did to the Japanese residents who lived there before). Portland seemed to will its ghosts away, but there are plenty haunting the mists and meadows around it.

Just another side effect of the housing crisis. No room for ghosts, it's already haunted by the living.