The decade following WWII saw mystery writers breaking free from the old rules and eagerly conquering new territories. The appearance of more flexible forms made it easier to write books that dramatically expanded the scope of the genre on formal, psychological, sociological, even political grounds. Suddenly it was possible and fashionable for a mystery to have no detective, or to deal with previously taboo topics, or to dispense with any criminal element. Being a product of the era, the Edgar Awards in their early years reflected the prevailing mood.
The problem with emphasizing innovation is that it's an extremely volatile concept, especially in as derivative/emulative a genre as mystery fiction. Critics who raved about The Horizontal Man and jurors who bestowed an Edgar upon it saw it (correctly) as a book that broke new grounds and played new tricks on the reader. As Eustis' discoveries went public domain, though, all that was left was an interesting but flawed book - an artifact.