Do you really think on-prem has more uptime than commercial cloud? For non-tech companies, no even close. Commercial cloud is adding nines to uptime and saving money by removing in-house IT admin staff.
the biggest miscalculation is really on expected uptime. People say they need 5 nines, yet take their car in for service twice a year for a tire rotation and oil change. How much uptime is _really_ required?