Those engines were really expensive to produce. Plus, the Guzzi *cogniscenti* of the day were largely unconvinced of the added value.
Head alloys became a significant development issue producing the 1064cc 2-valve big block with the Crane cam. So, perhaps, the V10 head alloys were an issue?
What a great motor (the V10) for those with the gumption to take it on! The Vee-eleven-slash-ten!