If you look hard at those early IBD cases, with rare exception, many of those cases were never confirmed via necropsy.
Without getting into too much detail (Alex and I fleshed this out in another thread), many of those early reported cases (cough cough Anapsid cough cough) were never confirmed with a necropsy and could have easily been something like OPMV.
Those early reports left an indelible mark on keepers. Now any time an animals shows neurological symptoms or a collection is ravaged by disease, the community immediately thinks "IBD".
The fact is that an animal can easily be am asymptomatic IBD carrier and die of something else...........