I think it's a combination of factors...their relatively small adult size and docile temperament boosting their popularity as pets, the ammount of time they've been available as a captive-bred species compared to some other snakes, the less rigid restrictions on imports and a lack of heavy predation in the wild all probably contribute to their diversity of morphs.

Whatever the reason, I'm glad of it. I see the Ball as a python for everyone...from the kid who has a normal as a pet to the breeder who creates stunning combo-morph designer-snakes after many generations of trial and error. If you have the money to take care of a snake, then there's a Ball out there in your price range...if you want a normal, I've seen them as low as $15 or $20. If you want a nice morph but can't afford too much, a single dominant or co-dom morph can be had for a couple hundred. If you want the Rolls Royce of snakes, there's Balls out there that people burn thousands and thousands on. I think that too contributes to their morph numbers...my first pet snake was a normal-phase Ball back in college. He was the snake that got me into constrictors.

I remembered seeing the Mojave, at the time a "brand new morph" (and before they had bred the Super Mojave), and thinking it was the most beautiful snake I'd ever seen...and daydreaming about how I'd have one in a heartbeat if I won the lottery and became a billionaire. Years later, rediscovering my love of snakes, that was the first thing I bought...a Mojave. It's a dream come true...or maybe a gateway drug, since now I want a Super Mojave, and a Jigsaw, and a Mojave Spider, and Cinnamons are delicious and I want a Super Cinny, and a Kingpin, and and and...yeah.

I gots the morph disease. Can't have just one.