Does anyone know why the census taker would make note of different houses/dwellings and not who was living in them (1870 Fed. census)? Was something happening in Holt County in 1870 or did a lot of the residents go somewhere else in the summer? Where?

I am trying to find Perry A. Duncan and family. They are in Platte County in 1860 and Holt County in 1876 state census. Can't find them anywhere yet. In going through the census page by page for Holt County, I noticed that there were quite a few blank lines and am wondering if he and his family is one of them.