Building equipment to withstand outdoor conditions is really, really difficult. Anything metallic corrodes, anything organic deteriorates, and anything flexible fractures.
The weatherproof boot on this outdoor sign switch has a tiny crack where the toggle enters the body. Not very big, but it’s the beginning of the end…
If the rest of the box had an air-tight seal, then things would get really ugly. Diurnal pumping can suck enough water vapor in through that little hole to eventually fill the entire box with water. Long before then, though, the electrical gadgetry will corrode.
Even though this sign seems to have plenty of openings around the lighted panels, the switch will eventually fail all by itself. Then they’ll likely throw the whole thing out; nobody fixes anything these days, right?
Here’s a detail view.