Why did the novel rise in the 18th Century?

Watt's thesis: 

Developing concurrently with a new emphasis on individual knowledge and perception (e.g., Locke, Decartes) as the source of knowledge and experience (e.g., the modern self), the 18th century novel, according to Watt, “purports to be an authentic account of the actual experiences of individuals” as they live out their lives in realistic settings (The Rise of the Novel 27). 

Cathy Davidson helpfully sums up Watt's accounts of what comprises this shift; for Watt, the realism of novels “operates on numerous levels: linguistic (characters sound as if they are talking to one another); situational (. . .within the time and space of fiction); and personal (characters are viewed as individuals not types” (Davidson 52)