Burmese pythons mature earlier, reproduce more readily, and produce a greater number of offspring per clutch.

Burmese pythons also suffer from a lack of popularity with the average herper due to their size as well, which puts them at a definite disadvantage price wise.

Also, the government is attacking the "large constrictor" market with a vengeance. Many people don't want to buy burmese pythons right now because they fear the repercussions.

I personally love burms, and put them much higher on my list of personal favorites than the ball python.

Hope that answers your question.