Why does the spread of sphagnum cause waterlogging in the area?

Swamping of an area occurs when high humidity is constantly observed in it and there is no outflow of excess liquid. Because of this, intensive decomposition of organic matter begins, and the area becomes waterlogged.
Sphagnum is very hygroscopic. It can absorb about 25-30 times more water than it weighs itself. Due to this property, sphagnum is widely used in the manufacture of various products, for example, it can be used to make a filler for diapers. However, in nature, this ability is not always useful. If there is too much sphagnum, it will retain excess moisture, preventing it from evaporating, which will cause high humidity and waterlogging of the area.