You have it a bit backwards: the energy demand has to do with the price of the coin. You can look at mining calculators to see what the relationship is between kWh and coins today, and some have historical charts. This relationship is baked in to the "difficulty" of the mining function and the block reward - higher difficulty means more hashes per block which means more watts per coin. In turn, your power company charges you per kWh, and in an efficient market, you are going to expand operations until your marginal cost (the cost of power) is equal to marginal profit (profit from selling the coins you mine). Generally, bitcoin mining has been done in such a way that if you have access to power at 5-10c per kWh, you can mine profitably (not including the cost of a mining rig).

As the block reward goes down (and it is dropping), the rewards of mining also drop, so you have a reasonable argument that the power use is transitory until the block reward goes to 0. However, it looks like this may end up being made up with transaction fees because the transaction throughput of bitcoin is also really low.

Lightning and other solutions are supposed to fix the transaction throughput, but they have limitations.