One word MUTATIONS, well at least to me.
If I was to breed my 2 dogs I would get more of the same unless I want to make mutts, and the rest goes for most animals, sure there are a few mutations in other animal species, but nothing like in BP.
With BP it is an unlimited world of possibilities (and challenge) for me and then you had the genetic factor which is fascinating. To me the are living art.
Thing is there are as many people getting into breeding snakes than there are dropping out because they are in without a true passion, without the right reasons and without a plan.