Because the village only exists because of drainage. Royal Palm Beach was created in 1959 out of what was primarily uninhabited swamp and natural preserve, and a massive drainage project was essential before anything could be built at all. The village still maintains its own canals and has installed French and inline drainage systems across it.
Ground that had to be engineered to hold buildings does not stop being wet ground. The water table sits close to the surface, so water escaping a pressurized line under a slab does not pool where it broke. It travels through fill until it finds a seam, which is why the damp patch you can see is evidence rather than a location.
The other local quirk is who is responsible for what. The county supplies the water and sewer, the village runs the stormwater utility, and some properties are served by the Indian Trail Improvement District or the Lake Worth Drainage District instead.