I don't think there's much of a rationale; nobody I knew in CA liked eucalyptus trees, they just are everywhere. I had heard they wanted to make railroad ties from them.
https://www.independent.com/2011/01/15/how-eucalyptus-came-c...
There are other Eucalyptus trees that are massive and perhaps less attractive, that I still find awe inspiring because of their massive size.
I did not know that they were such a problem in wildfires, despite being born in and living nearly the whole of my life in Southern California. You learn something every day.