Or do you disagree that planning for a total failure of one and running redundant workloads on other vendors increases your costs 99.99999% of the time? Because that's a fairly standard SLA from each of the major vendors. Let's even reduce it to EC2's SLA, 99.99%. So 99.99% of the time you're paying 3x as much as you need to be paying just to maintain your services an extra four hours per year. Again, you can disagree with that but that doesn't make it incorrect.

Some businesses might need that extra four hours, the cost of the extra services might be cheaper than the cost of four hours of downtime per year. But you're not going to find many businesses like that. Either you're running completely redundant workloads, paying 3x as much for an extra 4 hours per year, or you're going to be taken offline when any one of the three go down independently of each other.

Single providers go down, yes. And three providers go down three times as often as one. Either you're massively overspending or you're tripling your risk of downtime. If multi-cloud worked, you'd be hearing people talking about it and their success stories would fill the front page of Hacker News. They don't, because it doesn't.

I’ve never heard of an untested failover mechanism that worked. Most places are afraid to invoke such a thing, even during a major outage.