The pooling happens when the temperature inside is a lot colder than the temperature outside..it's called Dew Point. Once you hit the dew point you get condensation, which then turns to a pool of water. This is exactly why I leave my drain hole open and don't use hardly any beads. It creates it's own humidity and needs to be able to drain the excess condensation or my RH goes too high.
Dr Joe has a great video going into depth about dew point and setting up humidors/wineadors. Check out his channel on youtube.....LOTS of valuable information and pretty entertaining...IMO anyways.