The ground surface is typically colder than the dew point temperature of the exterior air. The underside of crawl space floor insulation is radiation coupled to the ground surface and is very close to the same temperature of the ground. Moisture droplets can be seen all over the top surface of typical polyethylene ground covers as well as hanging from the bottom surface of the crawl space floor insulation. It must have leaked through the walls. Give me another break.
Moisture moves to the cold surface.
Venting crawl spaces made sense only when you had no air conditioning and no insulation and no crawl space walls. This is a no brainer. Negative air pressures in buildings in hot, humid climates induce infiltration of hot, humid air. Leaky ducts in vented attics and vented crawl spaces lead to negative air pressures. You can never clean them.