The power grid is in fact a graph, not a tree, and not a grid. It
is automatically able to route around failures, and it does route around the failures. These failures happen every day, but people almost never notice. Almost.
The trouble is that the power grid just operates on the electrical principle of electricity following the path of least resistance. So if there's low resistance but low capacity line between generation and usage, the electricity will flow through it, and there is no QoS on the line that can limit how much power goes through it, besides on/off.
The on/off nature of the interconnections is what makes the power grid fragile. If a interconnection has a rating of 100MW or whatever, and the grid attempts to pump 110MW through it, you either leave it on and hope it doesn't break or shut it off and pump 0MW. The grid will then automatically route that 110MW through other interconnects. If there is a nearby 500MW interconnect that is currently pumping 350MW, you're fine, but if it's pumping 475MW, you're probably not. This can lead to cascading failures.
The grid does have the ability to shut down usage if there's a danger of a cascading failure. For instance, if your 100MW rated interconnect has 101MW coursing through it, you can shut down a neighborhood that's using 10MW or whatever, and keep the 100MW interconnect online with just 91MW running through it. This is what brownouts and rolling blackouts are.
The grid can have major failures, but these major failures don't happen unless there are multiple overlapping minor failures. Similarly, if your 737 MAX has 2 MCAS sensors and 1 manual MCAS override button, and both your sensors and your manual override all fail, you're going to have a bad time. Look at the sequence of events of the 2003 Northeast blackout: https://en.wikipedia.org/wiki/Northeast_blackout_of_2003#Seq... There are at least half a dozen failures between the initial problem at 12:15pm and until the point of no return failure at 4:05pm that if handled properly would have averted the crisis and turned it into a minor inconvenience. At least half a dozen instances of human error plus multiple instances of equipment failures. If an aircraft had that many things go wrong all at once, the plane's going down.
Note that the Texas power outage last year wasn't like this at all. The grid actually kept working fine, the problem is that there were lots of generators that failed as a result of the cold, mostly due to impure natural gas freezing. The generation capacity of the grid was cut to a fraction of its capacity, and as a result, they shut down a bunch of cities to reduce load. For whatever reason, they just left power off in several cities for days instead of doing rolling blackouts. I don't know enough about the circumstances to speculate on what the reason for that is.