Domestic servitude in this era was often sort of a hereditary thing. If your father was in service, you likely would also have entered service. The same idea as the son of a blacksmith or baker following in the footsteps of his father.

However, being hired in a noble or royal household often depended on a reference from a current or former servant. Male servants were considered a status symbol as they were paid more. Footmen were also chosen for their looks. Daniel Pool, the author of What Jane Austen Ate and Charles Dickens Knew, writes: 'livery,' or household uniform of fancy coat, knee breeches, stockings, and powdered hair, a costume that endured to the end of the 1800s. Because of their appearance at dinner and in public with the family, footmen were supposed to be the most 'presentable' of the male servants. They were evaluated on the basis of the appearance of their calves in silk stocking, and they often gave their height when advertising for positions in the paper–it was considered absurd to have a pair of footmen who didn’t match in height. (Poole, p. 221)

[This page] (http://www.thebookofdays.com/months/jan/12.htm) details the duties and touches on the evolution of footmen up to the 19th century.