Acronyms typically only are made up of a couple words which makes the capitalized abbreviation to be aesthetically pleasing in the context of a sentence. Quantas has seven letters which, if capitalized, would cause it to appear like emphasis is being added to a single word. For example, I'd much rather look at Roy G. Biv than ROYGBIV.
Not everyone knows or cares that Quantas stands for something. It is a strong brand. It is easy to recognize. It does not make a difference if people do not know what Quantas stands for. Therefore, people do not need to know that Quantas is an acronym. Therefore, there is no reason to capitalize the name.
Quantas have been using that name fr many years now and that is how they chose for it to be written. There is no need for someone to request they change it, just for the sake of correct grammar. The text would look strange it some of the letters were capitalized and some were not.
No, the Quantas name is catchy and pleasant, and it was the right decision to only capitalize only the first letter of its name regardless of whether it is an acronym or not. The name of this airline would not be nearly as aesthetically pleasing if all of the letters had been capitalized.