Woodlice have no teeth.

They can exist in cavity walls if there is any suitable material - birds nests, wood, which will most likely be damp enough at its surface to sustain them. Then they can make their way inside - such as around or through the ends of your joists :-)

They can exist in kitchens & bathrooms, or underfloors where a chimney vents to the under floor and lets moisture in (often directly if a pepperpot chimney cap).

If you are finding dead woodlice, they are coming in from somewhere - which may well be outside - and then finding no food source inside.