Earth Based Plots are the method by which the production of Doctor Who saves money. Expansive sets, intricate CGI, and clever use of video effects can be expensive, and there's only so many times you can make an alien planet out of a gravel quarry. As a result, why not take a film crew, a character actor with a substance abuse problem who really needs a day's scale wage, and some key grips in silly costumes, and go for a wander in the streets of London, or Cardiff, or along the backroads of the welsh countryside?
For some reason, the novels decided to stick Eight on Earth for over a fucking century even though they didn't have to worry about budgets the way the TV show did. This mostly involved him fucking famous computer scientist Alan Turing and adopting his own future daughter, because why not.