I notice you never hear about a blackout due to a gas or coal burning generator going down.
Then you haven’t been listening.
The problem with the U.S./Canada grid is the failure to build capacity to keep up with demand. We buy more and more electronic toys and import millions of energy using immigrants and try to hobble by on a grid built in the first half of the twentieth century. The luddites oppose any new generation plants or distribution lines and the politicians brow beat us with claptrap about the environment instead of getting out of the way.
I firmly believe that without government interference energy, health care and education would all cost about half of what they do right now.
Hydro systems are extremely simple...the water flows through the turbine, spins the blades on the generator...and voila, power.
There is something the authorities are not telling us about this outage. I would guess that someone took out some part of the distribution system attached to the dam...either by explosives or cyber-warfare.