Genuinely interesting pattern you've picked up on there. I came across something similar when I was reading through older sighting reports from the US Midwest - quite a few of them clustered around disused rail corridors and I never really thought much about it until now.
My first instinct was that its just a practical thing, like the tracks create clear pathways through dense woodland so both the creature and the witnesses end up there for obvious reasons. But then I started wondering if there's something more to it. Old rail lines often follow natural geographic features, river valleys, ridge lines, that sort of thing. Could be those routes align with something older, territorial paths or ley line type corridors if you want to go down that road.
Also worth considering the infrastructure itself, iron and steel, some traditions hold that certain entities have strong relationships with iron. Not saying I buy all of that fully but it seems worth exploring.
Has anyone cross referenced specific sightings with maps of abandoned lines? That would be a solid starting point for actually testing whether this is a real pattern or just confirmation bias doing its thing.