Interesting thread, though I'll admit cryptozoology isn't really my patch - I'm more of a shadow phenomena researcher myself. That said, the rail line correlation is worth examining properly rather than just pattern-matching anecdotes.
Old rail corridors share some fairly mundane characteristics that could explain elevated encounter reports: they're linear green corridors through otherwise developed land, they concentrate wildlife movement, and they attract a certain type of lone nocturnal wanderer (your urban explorers, your photographers, your insomniacs). More witnesses in isolated liminal spaces = more reports. Doesn't necessarily mean anything is there.
That said, I'll throw this in because it's genuinely curious - there's documented research suggesting electromagnetic anomalies cluster around old iron infrastructure, particularly Victorian-era rail beds with intact ballast and metalwork. I've picked up some genuinely weird EM readings near the old Scarborough line remnants up here in Whitby using a TriField TF2. Whether that has any bearing on perception-based phenomena or actual cryptid activity, I couldn't say, but the infrastructure-anomaly link isn't completely without merit.
What I'd push back on is the assumption that ". More sightings". Means a real population increase. Has anyone actually mapped these reports against population density, access points, or active enthusiast communities in those areas? Because without controlling for witness distribution, you're not really doing research - you're just collecting ghost stories.
If someone's done proper georeferenced data on this I'd genuinely be interested to see it. Otherwise we're speculating into a void.