People do not understand how extremely large the world is. The West Australia coast is around the same as if there were a coastline from Galveston running all the way around to Seattle. The State is around as big as the USA West of a North South line running through Galveston to the Canadian border. The entire state has a population of around 2.5million which is a million less than the population of Los Angeles and most of that population is in Perth. The chances of wreckage being found by someone who remembers MH370 is extremely small. The coast is covered with flotsam and jetsam of all sorts. Only if a sizeable piece of aircraft turned up on a beach might anyone notice and that is a long shot.
If you wanted to lose an aircraft dropping it into the sea over a thousand miles West of Perth into unexplored areas of the South Indian Ocean would be the ideal choice.