Because what I consider neglect and what you consider neglect can be two completely different things and snakes are extremely adaptable and variable.
Most captive snakes are overfed, there is no standard for what a healthy weight is at a particular age.
Take a wild snake and a captive animal of the same age and just about every time the wild snake is going to much smaller and thinner as well, does this mean the snake isn't thriving? Not necessarily.