i think it's a self-fulling prophecy because they are scared to take the risk, and since no one is taking the risk, theres little to prove it can work. It's why I think small harlequin sized releases would be good for more weirer stuff - and personally id be perfectly happy if it was only 1 small faction like that with one or two kits.
Also, Maybe to dudes, but i dunno - all the girls i talk to seem to really love the weird/creepy stuff and find all the humanoid stuff boring (a lot of girl 40k gamers seem to pick nids too) - but I admit that thats ancedotal to be fair, and they are the sort your more likely to find at a skinny puppy concert rather than a GW store :P The best arguement "For" them is probably Daleks which are arguably one of the most (if not the most) profitable SF alien baddies of all time.