On the flip side, demand is largely inelastic. The lack of real time metering means that we don't know how much we use or indeed how much it costs until after the fact. For the consumer, electricity is not something we think about, much less deliberate over. We do not usually decide when to use electricity. Thus we cannot react to high prices easily by cutting consumption.
Demand is also highly variable within the day, causing great fluctuations in hourly prices.
The short term inelasticity of both supply and demand is the main reason for price spikes. The delivery of power is also subject to transmission capacity constraints and the requirement for grid stability, further limiting the availability and flow of power. Transmission constraints can cause the formation of load pockets. Plants located in such areas have price-setting ability. When you need power the most, that's when everyone else also needs it.