We don't "always" use botanical names but, you're almost right. The problem is that the majority of Australian plants just don't have accepted common names and, in many cases, common names that do exist can apply to two or more totally different plants.
For example, "Native Fuchsia" can apply to either Epacris longiflora or Correa reflexa, depending on whether you live in New South Wales or Victoria...and the two plants aren't even closely related (except that they're both plants!). To confuse the issue even further, Eremophila maculata is sometimes called "Native Fuchsia" also!
|Correa reflexa (left) and Epacris longiflora (right).
Does either one really look like a fuchsia? Photos: Brian Walters
So botanical names are used to minimize confusion and, while there are a few "tongue-twisters", most aren't that difficult. Is it that much harder to pronounce "Melaleuca" than "Honey Myrtle"??