Tofu absorbs excess water in the fridge because it's porous and sits in its own released moisture, leading to a soggy texture. Proper storage techniques can minimize this.
Tofu is essentially a sponge made from soybean curds. Its porous nature allows it to easily absorb liquids. When stored in the refrigerator, tofu releases water. If the tofu is sitting in this released water, it will reabsorb it, leading to a higher water content and a softer, sometimes mushy, texture. This is especially true for softer varieties of tofu. The longer it sits in the fridge, the more water it tends to absorb. To prevent this, you need to minimize the tofu's contact with its own released moisture. This can be achieved by regularly draining the container and using methods to press out excess water before and during storage.
To prevent soggy tofu, wrap it in paper towels and place a weight on top to press out excess water before refrigerating. Change the paper towels daily to keep the tofu as dry as possible.