Condensation ONLY occurs when humid air is subjected to a temperature below its "dew point". In the summer time, when it is humid, the temperature is ABOVE the dew point.
Yeah, the above-ground temperature. Below ground is usually a fair bit cooler than above-ground. Above-ground air subjected to below-ground temperatures = condensation.
HOW does the humid air get into a "sealed" circuit
Wet-location rated boxes & conduit aren't vapor-proof. That's a whole other level.
and even if it does how does ENOUGH air enter to cause more moisture than evaporation would eliminate
I'm sorry, but that question isn't making sense to me. The amount of condensation vs evaporation, is related to the total amount of air movement... how? You have it exactly backwards. If there was enough/more air movement, the conduit could dry out.
Compare to wall cavities - back in the old days, before insulation, the inside of the walls would get damp, but because there was a lot of air movement in there, they'd also dry out easily. It's only nowadays, with our tightly-sealed construction & cavities stuffed with insulation, that we get condensation problems in walls if we aren't careful.
and even if it gets in, HOW does it circulate enough to pass through the pipe in order to be subjected to the low temperature? Now THAT is "voodoo science".
Again, compare to wall cavities. You only need a teeny-tiny hole for enough air movement to transport a whole lot of moisture.
I got one for you - electrical boxes on the outdoor lighting, on Fire Island? Have to be checked out every year. Saltwater air gets in, vapor condenses inside, then water evaporates out I guess - they're usually dry inside, but also usually half-full of salt.