Only way to tell if an operator isn't watching the gauges is after the machine is broke down in an area related to the gauges
That's an easy conclusion to jump to, but a gauge, (nor any other sensor-activated warning or shutdown), responds to conditions before they occur. A temp gauge creeping up is one thing, but what about instantaneous failures like oil pressure dropping to zero? If it drops to zero, a failure or breakdown has already occurred....you gonna blame your operator for that?
For a lot of applications, a switchgauge seems like the ideal situation to me. A warning lamp/alarm goes off as the attention-getter, and if the operator doesn't throttle back and shut down within the time frame the Murphy switch timer has built in.....then it shuts the engine down for you.
I'm not against monitoring gauges, but what about common, everyday uses like running your tractor as a power unit for an auger/generator/whatever? Do you always have someone in the seat staring at the gauges? What if the equipment being used doesn't have a seat for the operator to sit in and stare at the gauges? What if it's a something like a genset or a pump? What if it's something like this machine below, where the operator is at one end of the machine, and the gauges are at the other?

Here's the operator station in the basket:
And here's the gauge panel....on the base of the machine. At the opposite end and turned sideways in relation to the operator station:
someone who cant look down at gauges and know the general operating condition has no place on a machine not owned by them.
No, these aren't tractor photos, but a lot of equipment is this way. Saying you'll hire/fire operators based on their ability or willingness to simultaneously operate the machine and stare at the gauges isn't often practical.