Not excusing the neglect of any snakes, but they survive in the wild despite all sorts of adverse conditions (weather, food & water shortage, predators, wildfires,
environmental pollution, roads/loss of habitat, roaming pets, etc). But there's a big difference between "survive" and "thrive"...I don't think you can truly say that
a neglected pet snake is "thriving" if it has had sub-standard care, even if the long-term effects aren't immediately obvious. It's a bit like humans who smoke...the
serious effects might not show up for a while, depending on their own genetic resistance. Or "stress" of any kind...a no-brainer, but a challenge to prove.
For anyone with the resources to take in (rescue) a neglected snake (or other animal), few things make you feel better than turning it's life around for the best.