Don't confuse faulty hardware with software abstractions of perfect hardware. Those cloud VMs are still running on some hardware somewhere, even it's been abstracted away from your control. And that hardware can and does fail.
They lost about 50k in sales that day, still less than the cost-of-ownership for redundancy.
PS. Please keep conversations civil. You probably don’t know me, but I’m the least “scared of failure” person you’ll ever meet.