Some would say, because it's cool, awesome, save, free, stable economy and political system or some other rational or personal criteria.
The interesting bit is that while all the above where true for me in the decision process of where to migrate, I think the moment I set foot on this land it became almost 100% spiritual. Not in a way that I would replace my Christian belief with something along "mother earth", it is more like "I think, I arrive at my destination, no need to go somewhere else". Strange thing, this feeling only applies to the country, "the land", not the people, For most of these I would, if I could afford it, buy a oneway ticket to the moon. Most of these people, although 5th or so generation of Australians, have a fairly hostile relationship with the land they live in. But hang on, that is a different subject altogether. Maybe another time.
Anyway, this strange connection to this country never even once made me want to go back to Germany. Life here is not glamorous or successful on the Hollywood scale of things. Only an inheritance of more significant proportions makes the financial side of our existence here  in Australia less of an issue.
Also, the first few years here in Australia I sort of felt like trapped or being in a prison. Fences everywhere and private land (including agricultural land) is exactly that, private. This means that as city slicker you can only move along the roads, between the fences. You see a hilltop somewhere and feel the urge to walk up there to have a look around, forget it, private land, the owner might shoot first and ask later what you are doing on his land. But when I get to place with no fences (or they are out of sight) I feel the magic of this land. It is a very harsh and brutal land, it will kill you without regret, if you are not willing to fit in and want to do it your way. Even if you try your best, the land will not love you. If you force it, the land will retreat and leave you stranded. You first won't notice because you think you are in control, but eventually you will end up with nothing, the land will just abandon you without offering you reconciliation. But if you have this spiritual connection with the land you know that you have not other option, your life won't be complete without the land. Rationally it doesn't make sense, that is why most people here in Australia are confused, they live here but don't have a connection to the land and feel like they don't belong , they have to make up reasons why Australia is a good place to live in and so forth. Even the white people, who say they would "look after the land" often don't seem to fully understand what they mean by that. They seem to sense that connection and its importance to their life but they seem to struggle with the consequences for their own life, as they mostly pretend that there are none.
Brings the attention to the Aborigines, they shouldn't have a problem with all this, but strangely from the outside it looks like they have similar struggles. While the white people (all immigrants in the last 200 years) seem to struggle with the connection to the land they are living in, the first people seem to struggle with the wold (society) they are living in. If you drive through outback Australia you don't need road signs to Aboriginal communities, just follow the rubbish trail and you will get there in no time.
But again, that is another long story.
So why Australia? Simple answer, because of the land. Not the people, the opportunities, the society, the you-name-it no, because of the land. You wondered about the picture at the beginning? It is a simple test. You see a boring picture of some trees in a forest or some magic beauty? Interesting aspect is, that while I took this picture, the magic was almost overwhelming, while looking at the picture now is not that strong anymore. Probably means that magic can't be fully captured, it can only be experienced.

" In Germany many years ago we were used having quite seasonal fruit supplies. The apples (part of dad's stable diet) were great during harvest season in autumn but slowly the quality deteriorated throughout the year. We had Granny Smith as imports from New Zealand from around Christmas, which tasted great as their flavor was different from the local varieties. Other imported fruits were available basically all year round but the taste was pretty ordinary, some even required additional sugar. So we were used to having all sorts of fruits that tasted quite average. Coming to Australia it was like entering paradise, the fruits were so much sweater that sometimes we even felt sick after eating too much. Dad praised the Australian sun and the short distance to the markets and consumers for the top notch quality of the produce. In the beginning there was also a lot of second and even third grade fruit and vegetables to be found, meaning overripe and damaged.
A lot has changed since those days. Everything now is first grade produce, also sometimes you can get stuff after its "use by" date, which is different to second grade produce. These days all produce has a significant longer shelf-life, meaning that especially the the fruits are harvested much earlier, or in other words premature. The best example is Australian grown kiwi fruits. They are like little rocks when you buy them. After 2 weeks on the kitchen table they are still as hard and only started to shrivel a bit due to moisture loss. If you try to eat one make sure you have heart burn medicine handy, as the sourness will eat right through your stomach lining. Give the kiwi fruits another 2 weeks and they reduced in size by about 50% with their firmness still intact. If you are lucky you get the odd one soft enough to test for edibility but most of them shrink further before rotting away without ever gaining enough taste to beconsumed. While I still every now and then try a batch of Australian grown kiwi fruits in the hope to find some than are tasty, I more or less have given up and retreated to buying fruits from New Zealand or Italy. Never thought that Italian kiwi can be better than Australian. But there is always something new to learn here in Australia. 

we will have a federal election coming up soon. That's one of the highlights in a democracy, but what if the politicians are like the members of a drum band? They all beat the same subjects in mostly the same rhythm and they all march in the same direction, it is all about money after all. Together they sound like something great but only because they all want the same, my vote. After they got what they want, they walk off into the distance, pack up their drums and go home.