Why was this not filmed on Guernsey???

A very lovely movie about books, authors, post-war London and the Channel Isle of Guernsey which suffered more from starvation towards the end of WW II than the rest of the UK. I would have rated it 9 stars if it would have been filmed on Guernsey. Too bad it was filmed in Devon and a few scenes in Cornwall which are both beautiful areas, but Guernsey has it's very own charm. We've been to Guernsey in 2014 and fell in love with this Channel Island. After having watched "The Age of Adaline" with Michiel Huisman, I checked his filmography and discovered his Guernsey project which was finally realized last year. But to my big disappointment it was never released at the movie theaters in Massachusetts, it's not available on Netflix and you can't get it at amazon.com. Fortunately my daughter-in-law ordered it from amazon.co.uk and gave it to me as a Christmas present. I watched it twice, the second time this morning with my sceptical husband. But he also fell in love with the beautiful story and enjoyed the bonus material as well. BTW Lily James looks a lot like the young Oona O'Neill, the great love of J. D. Salinger who shortly after married Charles Chaplin. I hope if they finally decide to make a movie about her life that Lily James will play Oona.