From experience it is not easy to keep a distributorship for such a small project running and supported when the games are made overseas by a small company. Supply to customers is not that hard, but you need the tech support behind the product and the spare parts to keep the warranty claims under control. With warranty support, as a distributor, you need to get paid for the work conducted. If the games are poor quality, or have no QA done at the factory, then the customers will blame the distributor.
For Stern, they have this process worked out from years of distribution. The other manufacturer - JJP - No one was interested in distribution.
The only way Dutch Pinball's game can be distributed in Australia is after they have released several titles and have their place in the market. They can't send out 20 games for Australia and hope they sell. that's why no one has put their hand up to become a distributor.