Being successful enough that any amount of downtime is an existential risk is a great problem to have. 99.99% don't have that problem; even huge successful businesses can survive unplanned downtimes (see: recent major outages).

It's far from table stakes and you can absolutely overengineer your product into the ground by chasing it.

"0 downtime" system << antifragile systems with low MttR.

Something can always break even if your system is "perfect". Utilities, local disasters, cloud dependencies.