The blue and green plastic bins are naturally brought curbside by the residents, making it easy for the crime-scene clean-up crews to sneak them away. Plastic does not burn in microwave assault. Houses and vehicles cremated down to white ash, immediately adjacent to flammable trees, brush that does sometimes brown and even burn is apparently deemed less objectionable than untouched (unless by slight melting via convected / radiated heat) plastic bins immediately adjacent to burned / cremated walls, buildings, structures.