The time spent on that (let alone cost, for companies with large amounts of data) far outweighs the cost when a single region has an issue of today's scope. And you said it yourself, it's a 'small benefit'. Small benefits sound like exactly the things not worth spending time or money on.
For as much as many companies have had issues today, the daily reality is that these same companies haven't been having issues all the rest of the time (or this wouldn't have felt so shocking) and are likely to be okay with an outage of this scope (plus, everyone's too busy making noise about the issues to be working normally).
It’s not a monopoly but it’s close.
I couldn't even name another provider except maybe Hetzner
You could also argue that YT is on GCP (to some level) and that would probably bump that number up much higher.
The vast majority of people hosting things on the internet are on these providers. But you get downvoted for pointing that out now.