It’s all about speed. A power grid must be perfectly balanced at all times, there no natural storage in a power grid. If large power supplier disconnects witho

It’s all about speed. A power grid must be perfectly balanced at all times, there no natural storage in a power grid. If large power supplier disconnects without warning, that impact propagates at the speed of light. Other suppliers will respond by reducing their frequencies to keep voltage up, this is caused by generators physically spinning slower and converting their physical momentum into electrical energy. As you can imagine the momentum of a generator is large, but the stored energy is small compared to the rate of consumption. So you need systems that can respond within milliseconds to restore some stability. Batteries are actually one of the few technologies that can do that, but mostly your looking at shedding load. Disconnecting a consumer can happen in milliseconds, after all you just need to flip a switch (admittedly they’re very large switches). Once you shed load, then you have the time you need to spin up you “dirty” power supplies. But even the fastest response suppliers take minutes (think Hydro), not milliseconds to respond. So they’re not viable for dealing with the initial shock to the grid.