How can Blender afford to be free?

How is it possible for Blender, a sophisticated 3D computer graphics software tool, to be offered free of charge to users? Given the complexity and extensive development required for such a program, one might wonder how the creators and developers sustain themselves without charging for the software. Are there hidden costs or advertising that fund the project, or do they rely solely on donations and volunteer contributions? It's intriguing to consider the financial sustainability behind the decision to make Blender available at no cost to the public.