If your system integrates with any external systems or APIs, it's likely they have downtime when one of the cloud giants are down, so sometimes being up is not so relevant. If your system is up but everything you depend on is down, how useful is that?

For (almost) entirely self-contained systems it can still be useful, of course. But everything wants to be interconnected to everything these days...

Which, given that downtime is inevitable, leads to you having downtime while all your competitors have uptime.

Have fun with that…