First of all, I now cover MS since this incident made headlines. If you are aware of any such incident from the other providers, I am interested.
Another argument is that more companies depend on MS more. Even in high-tech startups and scaleups you'll find traces of Win machines, AD and Office. On the other hand, there are plenty of companies that don't have AWS deployments at all.
AWS is just a hyperscaler, they don't do the full business stack outside that. Google has a full business stack (read: office tools, email, hyperscaling) as an option, but the experience is miserable because Google constantly deprecates and changes things on a dime, which is why most people avoid them. Killedbygoogle stuff doesn't just apply to their non-paying customers, it applies to their paying customers as well. The moment you try to build anything outside of Gmail or Google Docs, you're subject to their whims and depreciation policies. (Case in point; Google has been sending me scare mails that they're going to kill an OAuth service I set up ages ago because it had no logins for 6 months. They just randomly decided it and gave me a month to deal with it. Their solution isn't just "hey, are you still active" - I am, that's easy to see - it's "just do a login and make sure you do a login every 6 months". If it was just a checkbox in their admin panel, I'd probably have done it without a second thought, but I really cba to figure out what the OAuth service was for, so I guess that OAuth service is gonna bite it now. Probably a selfhosted git forge or something that offered easy Google logins?)
Apple has everything except for hyperscaling, but it's all aimed at normal users, not corporations; I'm pretty sure they don't even have a business version of iCloud? The closest is that they offer MDM and bulk buying individual plans afaik. (Facebook isn't in this industry at all.)
Microsoft is the only one who offers a full kit and the promise that they won't pull the rug out under you. They're also the only one that really tries to take legal compliance and depreciation timelines/upgrade paths seriously. (AWS and Google just pass it off onto the customer with a "figure it out", while MS has loads of infrastructure for both of these.)
It's a hard business to replace if Microsoft goes bad with O365/Azure.