I'm not certain they are all that more difficult than some other species, but because there are very few successfully hatched in captivity, the export quotas from Madagascar basically mean we don't see them available very often, their wild populations (as are many other cham species) are at risk due to deforestation, poaching, and collection, and they have that aura of rarity and value, their prices are extremely high. They are really large which means you need a lot of space, a lot of water, a lot of larger food, pretty exacting climatic conditions to keep one healthy so far from their native habitat which all translates into an expensive animal to keep. They mature slowly and live a longer time than many species. Those few who have been lucky enough to breed them are understandably careful about the fate of their babies and don't tend to just plop them onto the market. You don't hear that much about them because so few of us work with them. Also I suppose no one wants to broadcast what they have to the web world just in case some thief targets them.
IMHO, there are other species I would consider even more valuable due to their rarity in the hobby...such as xenorhinum, malthis, willsii, balteatus, some of the really obscure montane African species...the ones there are no export quotas for, no population information for, and just about nil in terms of successful husbandry or breeding info.