They are considered beginner because whether you believe it or not Ball Pythons are not hard to keep IF you do some research prior to making a purchase and know what you are doing. (just like everything else you can keep)

They are considered beginner snake due to their size, temperament, and ease to handle.

Yes colubrids are good beginner snake too however they have a different temperament and the handling experience is not the same and not as appealing to some, I don’t even talk about their tendency to musk when and the nipping of young individual.

I have no issue with people owning a BP as their first snake and would recommend them to someone who is looking to purchase their first snake of course it would depend on their age, expectations, ability to meet the animal’s needs and how much work they want to put in it.

Whether or not a snake is a beginner level snake, is a combination of commitment, husbandry, disposition and size of the individual, it’s not all about one thing.