It comes down to popularity. Australians provide a massive amount of viewership for Eurovision. The EBU invited The SBS to sort out Australia’s entries. Lucky the SBS has been a long time partner of the EBU. It’s all to do with the EBU not the geographical area of Europe which is why Turkey and Israel are in it.
I wouldn’t say 300,000 people is a massive amount of viewers, especially in a country of 26 million. It’s the most watched program on SBS, that’s true. But SBS is small, so anything special would kill it on SBS.
I completely agree with most of what you said here except maybe the massive amount of viewership part. During the live performances Australia doesn't really have a lot of viewership, it's probably about 50 000 people watching the live shows, the timing is just really bad but the repeated prime time shows gets a lot more viewership. I think Iceland being so much smaller gets a bigger viewership than us and I even think the US probably has a bigger live viewership than us considering their population is much bigger than us but Australians are definitely crazy about Eurovision and SBS and fans have been following it for a very long time. I've been watching it for about 15 years now and love the fact we can vote in it.
If non of them competed, it would be the boring contest tbh. Plus countries like Lebanon, Egypt, and Palestine can actually compete if they wanted to, but of course they don’t want to. Morocco has competed once, there is a chance they could rejoin