Many families to each building - very high death rates. Any one who could afford to began to move away from the city center. By 1860s-1870s issues of public health and safety becoming important. Even suburbanization could not protect the rich form epidemics of disease like flu and diptheria etc. All local economies must have some basic sector activities in order to continue development.
Manufacturing is generally a basic activity that can generate the basic wealth of a community.
They function to circulate money about within the community, but do not generate it. An example might be a floral shop or locally owned restaurant. Most exploitive activities are in sales, but they can also be extractive, such as mining or forest products companies. Examples include national chain fast-food restaurants, national chain sales outlets for a wide variety of products, including motor vehicle fuels, groceries, and home improvement products. Began before the trucking industry really got going - was able to grow on suburban rail lines.