There's a flaw in your question, which is the assumption that mass migration of poor, starving Europeans to Australia to cultivate that land did not happen. This is a flaw, because mass migrations of Europeans to Australia in order to cultivate the land absolutely did happen in the 18th century.

Over half a million people emigrated from the Atlantic Isles (i.e., Britain and Ireland) to Australia between 1850 and 1860, very many of them Irish, and very many of them in response to the famine. And more emigrated later on - in fact, Ireland's population shrank from 6.5 million to 4.4 million between 1850 and 1911, mostly as a result of huge amounts of emigration to Australia, but also, of course, to North America (a much closer destination than New South Wales, which is close enough to Ireland's antipodes), where St. Patrick's Day is celebrated both by people both associated with the 19th century diaspora from Ireland and not.

In fact, Irish emigration to Australia is often seen as a contributing factor in Australia coming to have a separate identity to England/Britain and coming to want to be federated as a country rather than a British colony. The bushranger Ned Kelly is part of Australia's national myth, for better or worse, and he was born in 1854, the son of a John Kelly who had been transported as a convict from Ireland to Victoria in 1842. Kelly and his family did indeed end up as farmers cultivating the land, first in Beveridge and then in Old Avenel. Peter Lalor, one of the leaders of the rebels in the Eureka Rebellion on the goldfields in 1853, had arrived from Ireland the year previously.

But if we zoom out from the Irish in 1850, Grace Karskens in the book The Colony argues that, for many of the people who put together the New South Wales colony in the first place, that cultivating that land was the main point of the colony (though there's also plenty of other motives for the colony, from the geopolitical to the sociocultural). The upper class of England believed that cities were dens of iniquity, and that they had a bad effect on who they regarded as the criminal underclasses, so the solution to reforming those underclasses when they arrived in Australia was to put them to work cultivating the land. This is thus what the majority of convicts ended up doing - working on cultivating the land (which of course was land that was stolen from its original inhabitants, who had cultivated that land in their own ways, and who were still around to fight back against that land being taken by force, thus all the frontier wars of the 19th century - unfortunately, for the British in the 19th century, this was a very very minor consideration in the taking of land to be cultivated, and they were entirely happy to downplay this occurrence).

In any case, the (European) Australian population exponentially increased over the course of the 18th century; according to official Australian government statistics, there were 5,217 European Australians in the country in 1800, 33,543 in 1820, 190,408 in 1840, 1,145,585 in 1860, 2,231,531 in 1880 and 3,765,339 in 1900.

The British government subsidised the cost of emigration to Australia, essentially to ensure that (for desirable emigrants) the cost was equivalent to the cost of emigration to Canada (another option for British subjects wishing to emigrate). From 1841 - and mostly in order to help populate the rapidly expanding pastoral land used by Europeans - immigration agents in the British agents were given bounties for people with particular characteristics, and their passages to Australia were heavily subsised: 'agricultural labourers, shepherds, carpenters, smiths, wheelwrights, bricklayers, masons, female domestic servants, and farm servants' (according to a 1997 paper by McDonald & Richards titled 'The Great Emigration of 1841: Recruitment for New South Wales in British Emigration Fields').

Elsewhere, a network of government assistance and parish-level charitable assistance in the UK helped subsidise the passage of those who might not have been wheelwrights. Haines (1997) specifies in an article titled 'The idle and the drunken won't do there':

To be deserving of assistance, candidates were required to demonstrate, however difficult their circumstances, the ability to maintain themselves outside the workhouse, and to exhibit respectable behaviour—by the standards of the local officials.

So yes, the British authorities actively encouraged people to emigrate in order to cultivate that (stolen) land - especially farm servants and agricultural laborers.

Hey there,

Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.

If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!