Because what you smell isn’t sitting up on the surface at all. As urine dries it leaves alkaline crystals behind — salts that work down into the cotton foundation, far beneath the pile you can reach with a cloth.
Those crystals lie dormant until the coastal humidity finds them. On a damp Boynton afternoon they pull in moisture, come back to life, and let the odor loose again — which is how a spot that looked handled roars back a week on.
Urine that has soaked into the foundation won’t sponge off the surface — the whole rug has to be submerged and rinsed through.
Dabbing at the surface leaves the crystals below untouched. To be rid of them the whole rug has to be soaked through and rinsed until they wash free.