True, but aren't there plenty of such regions around the world? In the US I can think of at least Hawaii and Yellowstone.
Not the greatest population centers, but power lines have a good range. Also, Iceland is making good use of its comparative advantage by doing power intensive production like aluminum smelting and bitcoin mining.
https://en.wikipedia.org/wiki/List_of_Cascade_volcanoes
...how deep do you have to go to get to the 400C temperature level on some of those volcanoes??
Also many hot springs could be potential GeoThermal candidate areas http://www.hotspringsenthusiast.com/USsprings.asp
That said, geothermal activity isn't confined to the park borders, and there may be a suitable spot outside of the park. But again, politics. Building a geothermal plant in the middle of natural gas country would be a challenge.
Small note about Iceland- My web host (1984) is located there, and the servers run on 100% geothermal. That, in combination with the stellar privacy laws, make Iceland a nice fit for me.
That said, I agree that it would take a lot to get anything like that built.