Mom has never had any real sense of smell, and since Dad started losing his due to COVID, the two of them never actually have clean towels, clothes, etc. Dad runs the washer without detergent, takes stuff out of the dryer still wet, and piles it on top of any actual clean laundry Mom may have done, so the bacteria and mold can recolonize it. Literally everything here has developed a fecal/rot odor, and apparently neither of them can detect it.
In combination with the constant food poisoning due to Dad's "dishwashing" habits, it's clearly making them sick - they keep dozens of bottles of Imodium and Pepto around, Dad nearly died of a gastrointestinal crisis a couple years back, they keep getting skin and nail infections - but they either cannot accept that there's a problem, or think it's an unsolvable one that they just have to live with until it kills them. They don't think there's a middle ground between "do everything themselves" and "move into a nursing home."