... Because they are not fit for more! Shame about the (many) money for 4 bags. The "seam" - cheaply! - Tears already at low filling with construction dust and polluted the Hepa filter. Unfortunately I have not found a suitable alternative bags, because the nozzle in the tank is considerably thinner than in other wet / dry vacuums. My opinion: Stay away. This also applies to the Nilfisk Multi30T, since there is only mW these bags for the part. Too bad, because the suction would be per se ok