Potentially infectious material
Blood can carry bloodborne pathogens. Because there is no way to know by looking whether a given sample is infectious, it is handled as if it is.
Where it goes
Blood soaks into carpet, padding, unsealed wood, grout, upholstery and mattresses. It also runs along seams and under baseboards where it is invisible from the room.
Why cleaning products are not enough
General household cleaners are not disinfectants for this purpose, and wiping a surface does not address material saturated beneath it.