Pulse-oximetry only alerts medical staff when breathing problems are advanced, and often too late. Yes, they’re cheap and ubiquitous. But they aren’t getting the job done.
Capnography
Capnography, which measures the carbon dioxide in exhaled breath, is expensive. It is only available for a fraction of the patients who need to be monitored.
Nurses
Nurses are too busy to do more than occasional spot-checks. These are done manually, and their records are frequently inaccurate. Patients are left unmonitored 98% of the time.