Why do bath mats with rubber backing fail in the wash?

Across r/BuyItForLife threads, the most common failure mode for chenille and memory foam mats is the rubber or PVC backing flaking off after repeated wash-dry cycles — one commenter said it 'ruined my washer.' Lower-heat drying and gentle cycles extend backing life. Long-term posters tend to recommend either a separate non-slip pad under a washable rug, or a cotton mat with no rubber at all.