An important detail here is that as imbalances happen it pulls the grid frequency around. Bad things can happen to various systems if the frequency goes too far out of range. Yes in theory all equipment should be able to trip fail safe, but in practice a power grid has a ton of inertia and there are limits to how you can engineer around that. Even if the grid blacks itself off safely with minimal equipment damage, bringing it back up is hugely more complex than just resetting the breakers on your house/apartment.