You might think that a power plant could easily start generating power, but in reality, only a limited number of facilities have everything they need to handle a black start. That's because it takes power to make power. Facilities that boil water have lots of powered pumps and valves, coal plants need to pulverize the fuel and move it to where it's burned, etc. In most cases, black-start-rated plants have a diesel generator present to supply enough power to get the plant operating. These tend to be smaller plants, since they require proportionally smaller diesel generators.

The initial output of these black start facilities is then used to provide power to all the plants that need an external power source to operate. This has to be managed in a way that ensures that only other power plants get the first electrons to start moving on the grid, otherwise the normal demand would immediately overwhelm the limited number of small plants that are operating. Again, this has to be handled by facilities that need power in order to control the flow of energy across the grid. This is why managing the grid will never be as simple as "put the hardware on the Internet and control it remotely," given that the Internet also needs power to operate.

The load-shedding that happened in Texas during the 2021 Snowpacolypse was (according to ERCOT) to avoid this precise situation. It was sold (somewhat retroactively) as millions being without power for a week was better than the months a black start could take.