It's all to do with the fact that māori in this region were quick to capitalise on the natural geothermal wonders that abounded.
Specifically, wealthy tourists travelled to New Zealand to see the famous Pink & White Terraces - located just outside of Rotorua. These were touted as the eighth wonder of the world at the time. Destroyed in 1866 by the eruption of nearby Mt Tarawera the focus of tourism shifted into Rotorua itself.