If decay has already set in the threat has likely either passed or isn’t something worth having a fight or flight reflex over (like toxic food or vapors). It’s

If decay has already set in the threat has likely either passed or isn’t something worth having a fight or flight reflex over (like toxic food or vapors). It’s likely just a natural process that’s useful in specific contexts (caretaking for babies) and doesn’t really affect fitness in other contexts enough to get selected out.