Why Japanese literature is generally pessimistic compared to anime works

This has a lot to do with traditional Japanese culture.

Japanese anime works are generally commercial in nature and are aimed at a different demographic than literature, so it's impossible to be too pessimistic. There is no market for too much negativity. But Japanese literature is different. Many literary works are not subject to commercial restrictions and are merely artistic expressions with more elements of Japanese culture. The problem here is very complex, but in simple terms with the "Tale of Genji" embodied in the traditional Japanese culture inherent in the "thing sad" idea has a lot to do with, let's say that Kawabata Yasunari's aestheticism works, by the "Tale of Genji" influence is very big, in his works always give people a kind of inexplicable sense of sadness, or, "mournful beauty". In his works, there is always a sense of inexplicable sadness, or, in other words, of "sadness and beauty". In addition, in some specific time range and Japanese society itself is also inseparable, especially around the Second World War, and by the Yankee "boy" and "fat" smashed, the Japanese people's spiritual impact is really very huge.