It's economies of scale - if Holden were selling a million cars a year here instead of 100,000 then the costs of development would be spread out and cars would be cheaper.
In the meantime, for a country of 20-odd million, we have one car manufacturer that produces large RWD sedans with a choice of a stomping straight six turbo or a supercharged V8, and another that bolts arguably the most easily tuned V8 in the world into a large RWD sedan and sells them at, in relative terms, bargain basement prices. The only equivalent car in GM's lineup now is the Caddy CTS-V which is BMW money over there.
Get on any Ford Mustang site in the US and see how badly they'd love to have the Falcon in V8 form. Seriously, they ache for a decent RWD sports sedan over there.