The issue is that “all the spots where they could hide” is absolutely any kind of crack or tiny hole. Floorboards were mentioned, and you cannot really take that away to clean it each week. Same thing for wooden beds: those have lots of spaces where a bug can go but not much else, short of dismantling the whole thing. They can also be in sofas, bedside tables, cabinets, chairs… And these places are not dirty, they are just available space. Fumigation is a way of getting rid of them because otherwise it is impossible to access the places where they hide during the day.