Multiple factors to think about..
* People spending less time outside at night in general these days, bc indoors is where all the gadgets are
* When you do go outside at night, are your eyes going to be as dark-adapted as someone from say 1850 might have been? Shorter walks between brighter places these days could factor in.
* Swamps aren't as common as they used to be; particularly in the early 20th century in the US, swamps were frequently drained to 'improve' the land. Not as much decaying vegetation near at hand.
* Virtually everyone that dies these days is either chemically preserved, or cremated, so not as much decaying flesh in the cemeteries