Long transmission lines are highly susceptible to Carrington Events and similar (the article is behind a paywall and I won't pretend to have heard of a Miyake event before). This is a big deal.

Electrical grids tend to use very high voltage lines for longer distances in order to reduce transmission losses. To make this electricity useable in homes, transformers convert the high voltage to lower voltage. These transformers are essential for electrical grids to work, and when connected to long transmission lines they're likely to be damaged or destroyed by these sort of events. They're expensive, there aren't a lot of spares stored, and it takes time and effort to get them back up.

There are also concerns that a "black start" would be very problematic, as most power generation facilities need grid power in order to start themselves up.

In the USA, NERC (https://en.wikipedia.org/wiki/North_American_Electric_Reliability_Corporation) uses their Critical Infrastructure Protection standards (commonly known as "NERC CIP" and pronounced "nerk sip") to improve bulk power generation and distribution reliability. I'm told that progress has been made on improving resiliency of the various power grids and in getting generation facilities ready for a "black start."

I'm ready at home for at least a week without electricity depending on the weather, potentially much longer with cooperative weather and gasoline being available. I'd love to have more capability there in my next home; perhaps with solar, small scale hydro, or some combination. But I'm a couple years away from being able to move.