Some of them definitely would have stopped by or at least sighted land, as you say, its baffling and virtually impossible none of them didn't see the continent. So why didn't anyone stick around? The Northern coast of Australia isn't really a top notch place to hang out and natural resources are not clearly abundant-- this is why a number of Indian Ocean islands like Réunion or Mauritius- which have evidence of human visitation prior to European 'discovery'-- never had settled populations, there just wasn't a need, or the people would might have wanted to settle a new land weren't the ones stopping by. Traders making the Indian Ocean circuit weren't looking for new lands to settle. Northern Australia just isn't an obvious place to want to do any more than stop by. Not to mention if your goal is trading in Southeast Asia, you might only stop by Australia if you got terribly lost or blown off course, its not a logical place to hang out.

So aside from thinking about why people would very likely have stopped by, but not stayed, we can look at what circumstantial or possible evidence we have. First, we know Torres Islanders frequently visited the continent, so there were definitely people crossing and spending time there. Second, there is also some material evidence, coins from East Africa and Dutch coins, found in Northern Australia that give credence to the idea that there was material exchange going on in the region possibly as long as ~1000 years (the African coins) but certainly after the Dutch arrival in what is today Indonesia ~400 years ago.