The difference is that boa species are thought to be able to be asymptomatic carriers for far longer (possibly years) than ball pythons. IBD research is still on-going, so any facts about it often have to be taken with a grain of salt, but if it is true that boas can be asymptomatic for years whereas pythons die quickly, it would put the ball pythons at far more risk from the boas than from each other as quarantine for even 3+ months wouldn't necessarily mean the boa was free of the virus.