My thought is they are a beginner species as opposed to a more advanced snake species. For example one that gets huge and needs more than an old fisk tank for an enclosure or needs water to swim, branches to perch or climb, specific food requirements and/or other specific husbandry needs. There are always the potentially dangerous snakes being either hots or just the big giant constrictors that could take the life of inexperienced handlers or family members. There are also the real fast and large snakes like a False Water Cobra. One would have to agree that those snakes are for the more advanced or experienced keeper. So in comparison a ball python would be a beginner snake when compared to the much more difficult ones to keep in captivity.

In my opinion colubrids are also beginners as they are real simple to care for but definately could wiggle away from an inexperienced snake handler with their quickness.