I Wonder Why (1920) by Alfred Scott-Gatty is a music score book with the words by Dorothy Bouviere and the pictures by W. Graham Robertson.
The pictures in the book feature mostly little boys and that makes the book unique among the works of WGR who are famous for his fondness of little girls. But looking at the pictures one by one helped me understand the nature of the book. First, the boys are playing in the nursery, then outdoors, and in the bed at night and meeting with an angel. Published in 1920, I believe the book was a sort of "Requiem" for the British soldiers who died in WWI.
WGR mentioned this book in a letter to his friend Kerrison Preston, "The Gatty-Bouvierie-Me book seems to be going well and is stocked at most strange, unexpected, places in London, such as Liberty's, and the Army and Navy store" (Letters from Graham Robertson, p53). Though WGR wrote "unexpected", it's no wonder they put the book on the shelves of Army and Navy Store.