Money is the key, not "interest".
When a specie is easy to export at very low price offer is ok, then demand is ok, even for a "difficult" specie.
When export become complicated the prices become too high. Combinated with a demand limited to "specialistes" the specie is not imported/exported.
The captive breeding problem is not a problem ! Captive breeding Varanus exanthematicus is virtualy nul. But this sp is one of the more exported WC reptile. The price is the key.