Well, when particle board sub flooring gets any water on it, which is common in bathrooms and kitchens, it degenerates into a mush over time. Cheaply built mobile living units have a lot of these problems. You go to the refrigerator, and your left foot goes thru to the ground.
Plywood subflooring holds up like a real floor.
parsy, who says floors are nice
Ah, ha! Thanks for the explanation.
sharon, who would not like to step into a hole in the floor.