As national income increases in a given country, the size of government as a portion of gross national product (GNP) rises and the range of services people expect the government to offer rises.
Simple measures of GNP and prosperity vastly underreport this.
The higher the average income of the people (as expressed through per capita GNP), the higher the tax rate.
GNP and "standard of living" measurements don't capture this.
I suspect it is both; GNP rises, so we buy more energy, allowing GNP to rise so we can buy more energy.
An ongoing debate is whether a high amount of energy raises a nation or region's gross national product (GNP) or whether rising GNP increases the consumption of energy.