Europeans did. The Dutch first encountered the northern coast of Australia in c.1606, the western coast in 1616.

The northern encounter was a product of exploration inspired by the spice trade in the Indies, which the Dutch (like the Portuguese and English) highly coveted because it was massively profitable.

The western discovery was a product of the same trade, but for rather different reasons. The Dutch sailed to the Indies round the Cape of Good Hope, beginning in the very last years of the 16th century. Their first route took them north to Madagascar and across the Indian Ocean, sailing against prevailing trade winds much of the way – adding months to the length of their voyage. In 1611 a ship carried further south than usual by storms discovered the presence of a strong easterly current that took it to the longitude of the Indies in less than half the time – and in more clement weather, too.

The snag was that, in the years before the discovery of an accurate way of measuring longitude, it was difficult to be sure when to turn north and steer for the Sunda Strait, which separates Java and Sumatra. Get that wrong and it was easy to go too far east and encounter Australia. If landfall occurred in unfortunate circumstances - basically at night – the Dutch ships of the time were in big trouble, as they had turning circles well in excess of 4-6 miles. Several ships (Batavia, 1629, Verguelde Draeck, 1656, Zuytdorp 1712 and Zeewijk 1727) and most likely at least one or two more were wrecked on the western coast or offshore islands as a result, so as well as being the first European discoverers of Australia (probably; there are still some who suggest that honour goes to the Portuguese, or even the Spaniards – try looking up the "Mahogany Ship"), the Dutch were also the first (unwilling) colonists.

It certainly wasn't the case, by the way, that Australia wasn't discovered by Europeans because no one thought it was there. On the contrary, prevailing geographical theory was that there had to be a massive southern continent out there somewhere - one far bigger than Australia was, in fact – in order to counterbalance the Eurasian landmass in the northern hemisphere. This putative continent was called "Terra Australis" and can be seen on old globes. When Australia was first encountered by the Dutch, they assumed they had found northern outliers of this larger continent. And, of course, that's also how Australia got its name.

Among many good sources, I recommend Gunter Schilder, Australia Unveiled: The Share of the Dutch Navigators in the Discovery of Australia (1976).

Can I ask why you are discounting the ancestral aboriginal discovery of Australia?