You are correct that Daniel Defoe's Robinson Crusoe (or The Life and Strange Surprising Adventures of Robinson Crusoe), published in 1719, was probably the first fictional British "bestseller" and was republished four times that year. Adventure stories told by a first-person narrator were quite popular at this time, and Defoe capitalized on that.
One of the reasons novels did not achieve huge popularity until the eighteenth century was the need for an efficient and cost-effective method of printing them. Unlike poems, for example, which could be easily written, copied, or even memorized, a novel required an actual book in order for it to be effectively read. It is rather surprising to think about now, but paper was not always cheap or available, and refinements in the printing press did not occur until the mid-eighteenth century or later. The amount of leisure time a citizenry had also impacted how soon and how significantly the novel became part of the culture.
Consider the Medici family and others--all rich--who collected books from all over the world, recognizing the value of the recorded word; once books become more accessible and affordable, everyone could collect and read them. As Robinson Crusoe says, “It is never too late to be wise.”