The land isn't free and arable land with good water is hard to come by.

Mangoes are not grown in the Tanami or Great Sandy Desert. They're not grown around Kalgoorlie (that relies on piped in water from far, far away), etc.

   Mangoes (Mangifera indica) are predominantly grown in the Northern Territory and Queensland, and when combined, produce approximately 95% of the total national crop. Mangoes are also grown in Western Australia, New South Wales, Victoria and South Australia.

crop map: https://www.industry.mangoes.net.au/resources/resources-libr...

The areas they are grown have tropical rainforest (Qld), vast Wetlands (those parts of the Northern Territory with fresh water crocodiles, swamps, etc), annual monsoons (Kimberley), etc.

But yes, we do have on point water management.