The number of serious CDN outages in the world are incredibly rare.
In fact, you can probably remember most of them if you were given dates.
Plus, going around the CDN can be very complex (depending on the type of content), very expensive (all of a sudden you have a massive data out network traffic that didn't exist previously), and not guaranteed to work (DNS updates can take longer to get to everyone than the actual CDN outage lasts).
There are places where it is worth it and useful, but for a lot of the sites listed it's not useful.
In fact, you can probably remember most of them if you were given dates.
Plus, going around the CDN can be very complex (depending on the type of content), very expensive (all of a sudden you have a massive data out network traffic that didn't exist previously), and not guaranteed to work (DNS updates can take longer to get to everyone than the actual CDN outage lasts).
There are places where it is worth it and useful, but for a lot of the sites listed it's not useful.