Why are there so many spiders in this house?

A recent study published in Nature (November 2017) looked at where spiders live in houses. Entitled “The Habitats Humans Provide: Factors affecting the diversity and composition of arthropods in houses” authors Leong, Bertone, Savage, Bayless, Dunn & Trautwein found in their study that access to the outdoors and carpeted rooms had more spider populations than house tidiness, pesticide use, and pet ownership. "Our findings suggest that the more opportunities arthropods have to get into a particular room in a home, the more diverse the arthropods in that room are likely to be."