So what's motivating the denial? I understand that it's easy to form conflicting opinions when most of the evidence is anecdotal, and different anecdotes have different endings, because it manifests widely differently in different animals... but the large scale denial, what's driving that?

Is it the fact python owners are basically a large population of potential future boa buyers, and this is terrible press for boas? So every time another python owner's collection is devastated by IBD, the boa people groan inwardly the same we groan whenever another dumb monster python owner gets strangled by his african rock, or another huge Burmese is found under somebody's house?