Not really sure but I will guess that it would have been when the engines started to become more widespread in general purpose roles. ie. domestic mowers, pressure cleaners. That sort of stuff. Companies would have realised that they could save money by stopping their engines from over revving and wearing out prematurely. Thus came the governor. May have been around previously for other roles though? Pretty sure steam engines had a governer to stop them from running faster than necessary
It wasn't that, it was to stop them from blowing up! Look at the flywheels on an old hit and miss engine, people die when those go bang. Even early industrial engines like my little J.A.P are far more substantial than your average modern Honda(actually, it's a tiny engine, but the flywheel would be a whole lot heavier and weaker!). Also, back then, getting an engine to run at a constant 4000rpm without snapping a crank or doing a conrod was a pretty special thing. Engines wore out quite quickly back then anyway, rebuilding them was like changing the oil. It's not like today where once the engine is worn out you get a new one, wear was just something that happened.
I've seen pictures of huge steam engines that have had flywheels explode, they flatten the large factories they're housed in and kill dozens, it's incredible.
Thanks
Hayden