So do you have TOU on your cell phone? I'll guarantee you that their cell system is built for peak load too. Truth is we HAD TOU for cell service. You could buy a plan with 2, 3, or more pricing tiers depending on time. The public decided it wasn't worth the money and hassle of never knowing what your bill was going to be. So sometimes even when possible TOU rates are rejected by customers. Even if it is technologically possible. The regulators incentivise the utility to minimize costs. At the generating level, for instance, this is done by building units meant to be run infrequently to handle the peak load. They are less efficient (typically jet engines repurposed) but offset the lack of efficiency by having low capital cost. IE they require very little physical footprint, no cooling lake/pond/tower, no steam system, etc. Lots of other examples but there are many ways to reduce overall costs.