Why are census tracts generally smaller in urban areas than in rural areas?

Census tract is a subdivision of a county having a maximum size of 8000.

Census tract are generally smaller in urban areas than in rural areas because of population, The larger the population density, the smaller the tract becomes and the smaller the city the larger the tract becomes, Because the population of urban areas are high and growth increasing, the census tracts are split making them smaller while in the rural areas, due to the low population density/decreasing population, census tracts are merged causing them to be bigger