Perfectly put, young Geezer.
Those shooters who appear in AGW and AG and shoot with both eyes open are simply doing what works best for them, and it doesn't require much thought to see why. Shutting out 50% of your field of view in any shooting situation beyond the strictly controlled environment of an indoor target range make no sense at all.
Plinking in your garden demands maximum possible attention regarding safety, and seeing as much as possible of what's going on around you is extremely important.
In a hunting situation, the same safety awareness applies, and in addition that non-sighting eye could also spot a better target.
In FT and HFT competitions, you can discount the 'better target' deal, but add the possibility of spotting a previously unseen downrange breeze moving a target reset string, leaves or foliage. That really could be the difference between a hit or a miss on a long range shot. An eyeball is also one of the most sensitive wind-detection units available to us, and it works way better when the eye is open.
All in all, keeping both eyes open when shooting our air rifles outdoors really is the way forward, and I'd urge those who have yet to adopt this technique to devote plenty of their lockdown time to developing it.
Stay safe, everyone, and try not to shoot like this --->