Too convenient now, but back when it was discovered, it would have been way more convenient if its contents fit the mainstream consensus at that time instead.
So, the mainstream consensus at that time was that the traditional date for deuteronomy should be replaced by a later date , based on historical-critical methods. These same dates and theories enjoy considerable love today. If the shapira fragments are a 9th century BC copy of deuteronomy, modern historical critical thoughts about the composition and dating of the pentateuch are wrong.
Edit: Not a consensus I guess but the documentary hypothesis was emerging in the 1860s and 1870s shortly before these fragments made their debut.
