Especially because, in the industrial context, you actually want to see the equipment! (But then, in an industrial context, everything around the equipment is white or silver or black, rather than natural colors, so a drab green does stand out.)
AFAICT from some research, the use of that shade of green to paint industrial equipment, itself originated as a private-sector cargo-culting of what was originally an accident of history in public-sector use: a lot of drab green camouflage(!) epoxy paint was left over from World War I, and worked perfectly well as an industrial one-coat anti-corrosion sealant over bare steel; and large public-works industrial machines like the insides of power plants don't need to be any particular color, but do need to be corrosion-proofed; so the specifiers of these plants went with what was available. (In other words, industrial machines are painted, literally, "armored-vehicle green." Same paint, at least originally.)
If states hadn't had that volume of green paint laying around, I'm guessing they would have just used the cheapest anti-corrosion paint they could lay their hands on... which would very likely have led to industrial equipment painted red-barn red. Farmers paint that color because it's the cheapest anti-corrosion paint to buy, in turn because it's the cheapest anti-corrosion paint to produce, in turn because the red is literally just "iron, powdered, and left out in the sun to rust." (Thus the name of the paint brand Rust-o-leum!)