Last week Microsoft suffered a major outage of their Azure AD authentication services meaning many of their customers couldn't access key applications. -
Microsoft is one of the worlds largest software companies, if not the largest, and is certainly not short of cash. So if all the resources in the work can't prevent this sort of thing happening there must be a bigger problem.
The real problem is the system architecture, as although Azure AD is a well run Cloud service and is designed to be highly available, it is still technically a centralised system. With a truly decentralised model single vendor outages are not able to bring down the whole system.