Our house is very dusty. This is the case for a number of reasons. Some carpeting holds up better than others. Depending on the amount of wear, it typically takes 8-10 years for carpeting to contribute to significant dust accumulation on tables, dressers, etc. Carpeting is a sink or reservoir for a variety of particles that are tracked in, shed from humans and pets, and settle out from various other sources.
Dust comes from other sources as well.
Moving air with time causes mineral fragments to be produced and become airborne in houses which have clay pipe heating ducts in the slab substructure. On wet sites, water actually deposits silt in the ducts. Dust may enter living areas from insulation being drawn through cold air returns which are located in attics. Cold air returns are under negative pressure. As such, they can easily suck in any materials in close proximity with poorly sealed ducts.