Cadillac Northstar normal operating temp discrepancy

Under normal driving conditions my 97 Cadillac Deville's coolant temp runs at about 190-192F. Experts say that that 190 up to 205 is a normal operating temp. If that is a normal operating temp for the engine then why is it set so that the high speed fan doesn't come on till the coolant temp hits 234 and rising? The the most catastrophic thing that can happen to an engine is for it to over heat. Why wait till just before overheating to turn the fan on? Why tempt fate? If it's good for it to run in the 230's then why does it normally run at 190 to 205? Splain Lucy.