The purpose of the Railroad Trust is profit - profit for the rich.
A trust is a legal corporation which drives out competition by owning all the aspects of a given industry, allowing them to set pricing at will. In The Octopus, the Railroad Trust, which owns the land adjoining its tracks in California, has allowed poor farmers to build their livelihood on that land, with the understanding that they will eventually be able to buy the land, along with the improvements they have made on it, at low prices. When the time comes to buy, however, the price is set much higher, crushing the resident farmers, and leading to their eviction. The rich get richer as the trust benefits from the improvements the farmers have made on the land, and the poor farmers are left out in the cold.