GM has Opel, Vauxhall and Holden as essentially identical companies making broadly similar cars. It needs to sort out what it wants from its brands and pitch them accordingly.
Vauxhall/Opel are the same company - one badge for the UK and one for EU.
Holden make the Cruze (a Chev everywhere else) and the Commodore (unique to Holden) - everything else they sell is a Chev everywhere else.
GM's brand strategy for cars is clear:
Chev at the bottom, Buick in the middle, and Cadillac at the top.
VX/Opel and Buick are becoming more aligned - they sell Insignias badged as Buick Regal in the US for example.
VX/Opel and Buick all have a round badge so it is easy to rebadge stuff - you may not think that matters but when it comes to styling and engineering a modern car it does.
There are a number of things that aligned to cause Holden's demise:
The sudden (in automotive terms) shift to SUVs - it takes years to develop a car, so Commodore was too far gone to change. The SUV segment is too fragmented to justify assembling one in Aus.
The GFC - which killed GMH's main export customer Pontiac, and stalled work on Commodore and its replacement.
The high AUD
High labour costs
Currency manipulation by the Japanese (to keep their automotive manufacturing viable)
One way free trade agreements - 0% duty on everything imported from Thailand, but Ford get hit with 40% duty when they export a Territory!
A very, very fragmented market in Aus - which leads to volumes that are too low to justify developing a unique car like the Commodore.
Lack of government subsidy to the level given to the industry in other countries.
A general election, which resulted in:
A new government which is too shortsighted to realise the importance of manufacturing, and refused to agree to support at a level which is well below that given in other countries.
So a perfect storm, but one caused by government stupidity over several years and leaders.
Which means Australia will no longer be one of a handful of countries capable of designing, engineering, and making cars.