I don't understand how people can't comprehend why dual cabs and SUVs are popular. It's pretty simple once you take out performance (like 99% of drivers on the road).
A sedan does nothing great, only everything well.
If you want fuel economy, and don't carry passengers often, you buy a small car (e.g. i30, with the seats down it has more boot space than my Commodore). Disadvantage being you get half the boot space of a sedan when you have rear passengers.
If you want to carry people, you buy an SUV. They're also quite fuel efficient now with the I4 turbos, despite weighing 4 tons. They are usually comparable to a V6 Commodore, some of them are actually better... and the downside is the fuel economy.
If you need a tray, buy a dual cab. You can still carry 4 passengers with quite a lot of room, fuel economy is about the same as the V6 Commodore's too, if not less such as the Ranger... why is the sedan needed again?
In all three situations you have the boot space, the fuel economy and the passenger carrying capabilities of the sedan... except it's better. Why would you go for the technically inferior car when performance means sfa to you? I say this as someone who has only ever owned Commodore's and Falcon's. The sedan is pointless in an era where engine bays are tiny and engines are very efficient, that's why they're a dying breed.