Hi there! Historian of political culture/national identity from the Netherlands here. You pose a good and interesting question, which I think I can answer to a fair extent.
So in the first place the post-1945 wave of Dutch immigration to Australia (and New Zealand) has to do with the effects of the Second World War on the country and the geopolitical position of the Netherlands as a global player.
In terms of the effects of the war, the devastation wrought on the country and its infrastructure was significant. Several of the most productive agricultural regions (Zeeland, South Holland, North Holland, and Brabant) had suffered extensive flooding, shelling, and bombing as part of operations on the country's sovereign territory. This caused land to cost much more, and simultaneously drove up consumer prices of basic food items on both the regular as well as the grey/black market. Moreover, much of the housing stock had been damaged, with little initial perspective on it relenting until at least 15 years after the war. This combination led to many young families - especially from agricultural backgrounds - to elect emigration to countries in the Anglosphere to staying in the Netherlands and facing the relative hardship of the Reconstruction Era (which lasted until 1960-1965 or even the 1970s depending on what demarcations you utilise).
In terms of the geopolitical position of the Netherlands, the Second World War changed everything. Where before 1939 the Netherlands was a second-rank colonial power with an increasingly diverse economy, the Indonesian War of Independence and devastation in the Metropolitan Netherlands put it at the mercy of its liberators. American economic and military aid in the form of the Marshall Plan would only delivered and continued if Indonesian independence was recognised, and hostilities would be ceased in the Archipelago. Effectively this stripped the Netherlands of its initial recovery strategy in the form of an economic boon through the intensified economic exploitation of Indonesia's material wealth (especially crude oil and rubber). The increasing threat of Soviet invasion into Western Europe remained credible well into the 1960s, requiring extensive British and American investments into the Dutch defense apparatus, so the Marshall plan became integral to any form of recovery post-1948.
Thirdly and finally, there was also a cultural incentive to Oceania. There existed a sense of "we-discovered-the-place-right?" with Oceania, given Van Diemen's expedition. Besides that there already existed some cultural ties in the Anglosphere dating from the 1840s-1860s. Early waves of agricultural emigrants from the Netherlands had settled in Canada/Northern USA, British South Africa, New Zealand, and Australia already from that time. Small Dutch communities seemed to have kept in touch with the 'vaderland' throughout the century-or-so until the post-Second World War. Moreover, expat communities were present in the Anglosphere in the realms of resource and mineral exploitation, the shipping sector, the sea/air travel sector, and increasingly in the civil and aerospace engineering industry from the early 1900s onward, which helped bind together a thinly threaded 'global community' of Dutch emigrants, expats ánd emigrés.
Then to bottom line it form the perspective of a 25-30yo Dutchman anno 1945. I would be:
The solution for this vexing problem? Go to the wide open plains of the US Midwest, Cental Canada, or the beautiful Gold Coast of Australia, New Zealand's South Island, or even South Africa and Rhodesia, and figure it out for yourself!
Main source is Joed H. Elich, Aan de ene kant, aan de andere kant. De emigratie van Nederlanders naar Australië 1946-1986 (Delft: Eburon, 1987).