What determines if a Eucalypt grows to a massive size? Three factors: the genetic makeup, the site, and disturbance history.

An article written in 1911, notes that Australia's Eucalypts, at the time, were the tallest trees in the world. One fallen Eucalyptus regnans was measured at 480 feet or 146.3m tall
https://trove.nla.gov.au/newspaper/article/271327377

People are awestruck by the size and age of giant Eucalypts. The oldest giant Eucalypts are 500 to 1,000 years old, depending on the species. Giant Eucalypts have abundant tree hollows of different sizes and shapes for a wide range of hollow dependent fauna. They continue to provide important habitat for many decades after they senesce, die and collapse.

The official Tasmanian Government tourism web site now has a special section on where to visit big and old Eucalypts: https://www.discovertasmania.com.au/experiences/stories/big-trees/

The WA and Victorian governments also promote tall and giant tree tourism:
https://www.westernaustralia.com/au/things-to-do/nature-and-wildlife/tall-timber-forests
https://www.parks.vic.gov.au/news/2022/07/26/00/42/the-forest-giant

Giant Eucalypt forests are major stores of carbon. The total carbon stock has been measured at 1,312 tonnes per ha in an old growth forest, called the Grove of Giants, in Tasmania. To put this in perspective: "This is the highest carbon stock recorded in Tasmania and is above the average estimates for temperate forest ecosystems in other parts of the world."
https://onlinelibrary.wiley.com/doi/abs/10.1111/aec.13407

Hydraulic failure and tree size linked with canopy die-back in eucalypt forest during extreme drought:
https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.17298