Why is Nasu so lazy? There are tons of story he can write about. It is sad to see he keep re realising Fate/Stay Night over and over again million times.
He could write about Future Emiya suffering or King Arthuria in the past
It took Nasu like 14 years combined for Tsukihime and FSN.
You don't need to write about everything. Sometimes it is better left to the imagination of the reader.