It could be literally anything from a failed health check and failed auto mitigation, to a routine failure that no one actually knows who to contact about anymore, to sabotage by a laid off employee.

It’s not really worth speculating about fired employees performance, but there’s probably internal chaos after yet another layoff round.

They were good at making themselves indispensable, until they were dispensed.

That depends on the reason. For example, did someone cripple a system on their way out the door to cause the outage? Is this some retaliation? If so it doesn't speak to the quality of what was built. I only use this example to speak to the wide array of reasons that could cause this. Without knowing the reason it's hard to assess anything.

Any large service consisting only of integrating 3rd party providers with 3rd party consumers is fragile.

Alternative hypothesis: someone had a backdoor and didn't take their layoff well.

Alternative alternative hypothesis: someone got laid off and told to work out the rest of their shift, and used their frontdoor access to take a massive dump in the boses desk drawer.

This is just pure speculation - we don't actually know why it went down.