Power stations can absorb power ( somewhat, limited by the cooling capacity of the generation plant, not the steam condensers) by deliberately increasing the rotor current so the generator runs as a synchronous capacitor, and cutting the steam feed to a low level, so the turbine acts as a turbo pump instead and actually heats the stem entering so it is hotter going out than in. As it is still non saturated steam this only increases the load on the cooling condenser, allowing the power station to be a very quick acting ( though insanely expensive) power limiter, so they can safely ramp down coal feed ( or handle the control rod lag on a nuclear reactor that will take 20 minutes or more to start responding to a step change in loading, and which will take hours to drop power level to the desired point) and steam generation to handle a reduced load. Then for a step change up that is enough that the remaining plant can generate without the synchronous capacitor they reduce excitation so it becomes a synchronous motor with unity power factor, only drawing a little power while still being available for ramp up fast.
Big generation plant is not something you can turn on and off fast, black starting a plant will take days before it gets up to full power, and even a plant running at low power with a single steam generator and turbo running will take hours to ramp up the rest to full power, you have to keep it spinning at all times and keep the cooling and lubrication running at all times or you will destroy it. A hundred ton rotating mass does not respond fast to any step change, especially if it involves a massive temperature change and your tolerances are in the sub millimeter ranges for many of the blade clearances. If you have a blade touch you will be replacing large pieces of plant. If you really oops it it leaves via the roof or the wall, and anything in the way goes with as well.