Discontinuation
Sprite was not a microkernel system, and suffered the same sort of problems as other Unixes in terms of development complexity, becoming increasingly difficult to develop as more functionality was added. By the 1990s it was suffering and the small team supporting the project was simply not able to keep up with the rapid changes in Unix taking place during this time. The project was slowly shut down by 1994.
Read more about this topic: Sprite (operating System)