The mushroom is soggy and releases water when squeezed.

Mushrooms are 90% water in comparison to Spinach or Cabbage which can have a water content between 91-93%. Due to the high water content, when you squeeze the mushroom water will come out. It is also very water absorbent and can absorb the condensation within the package. Lastly, if the mushroom is damaged it will deteriorate sooner and release some of its moisture.