Same reason a 20oz bottle of water is $1.30. People are willing to pay for it.

As for the main question: I shoot pratically all brands/types of powder. I like them all for various applications. If I were only shooting scoped inlines with sabots, yes BH would be my #1 choice. Cleanup or swabbing doesn't bother me, I just prefer the consistency/accuracy from shot to shot that I can't seem to get with other powders (personally).