All the BP morphs are inbred to some degree. Some morphs more than others. For example, I believe all spiders and spider crosses descend from one wild-caught male. Breeding one male to many different females doesn't make for a very diverse gene pool -- you still have half the genes coming from one snake. There's no guarantee bad things will happen with inbreeding, you're just way more likely to have two "bad genes" come together with inbreeding -- just like you're more likely to have recessive genes for cool morphs come together in the same snake.

Just like in dog breeding, ball pythons have two genetic strikes against them: "popular sires" and "insufficient founders."