This is a great question. A renovation is a full overhaul of your existing bathroom, starting with demolition and a blank slate before altering the layout, adjusting the plumbing and electrical locations, installing all new linings and waterproof membrane, and bringing everything up to current Australian standards.
Bathroom furniture items (often called fixtures and fittings) are replaced with newly selected models that are specifically chosen by you, which look better while also saving water and energy by running more efficiently. Your new bathroom will look amazing but will also have been redesigned to maximise space and be perfectly suited to your needs.
A makeover, conversely, is making improvements to the existing space such as fixtures and fittings already in the bathroom. This will typically include things like changing baths and sinks, painting and replacing grout. It is usually not a fix for waterproofing issues, non-compliance with plumbing and electrical standards, or a non-functional design.
We often say that a makeover is like simply repainting a 1970s car (complete with its older standards and wear and tear) and calling it new.
Many licensed builders, including ourselves, will only work with full renovations as this means we can ensure that the finished space is functional, waterproof, high quality and built to last many years. Thus, being worthy of our name.