I would have to say Availability is the key factor. I'm new to the herp scene, but in the last 2 months or so I've stumbled upon hundreds of sites/people selling various pythons and boas. I few sites selling aborneals, yet I've never even heard of the ones you've named.

What makes them available?
I have no idea, maybe how easily they're found in the wild or how difficult it is to breed. Maybe some don't do as well in captivity.