There are multiple reasons. 'Robinson Crusoe' has a long - form narrative that follows the life of one character over an extended period. It has elements of realism, as Crusoe's struggles on the island seem very believable. It also has a psychological aspect, as we see Crusoe deal with loneliness, fear, and hope. These elements combined - a detailed character study, a believable story world, and psychological depth - are what set it apart as the first English novel. Earlier English literature didn't have this combination of elements in one work.
Well, there are several factors. First, the way it focuses on an individual's story in a very detailed way. We get to know Robinson Crusoe as a real person with his own quirks and growth throughout the story. Second, the use of a fictional setting, the deserted island, which is described vividly. And third, the exploration of themes like survival, self - reliance, and human nature which were not explored in such a combined and in - depth way in earlier English works. So all these aspects together make 'Robinson Crusoe' the first English novel.