This is based on reading the movie's synopsis on wikipedia but it seems to me that the big difference between the Frankenstein movie and novel is the the lack of development of Frankenstein's monster's character in the movie. In the novel there is the section where he learns how to act like a bourgeois  from the De-Lacy family and is able to speak fluently and be intelligent. Meanwhile in the movie he seems like he is strictly a monster is the generic sense with a small sense of humanity when he is playing with Maria. For the novel you can blame the transformation of Frankenstein's monster on the rejection from society. For the movie the monstrous identity is instead blamed on a criminal mind. In a sense the movie is implying that society has little or not part in playing in the monster developing a animosity towards human beings.

I believe it was a conscious decision because how Hollywood has managed to embed the idea that the name of Frankenstein as the monster. I believe the context of the film in history and the time period was the cause for the Frankenstein's name being so tied to the monster and not the scientist. Before the screening of Frankenstein there had been many movies in which the monster in the movie is the title. Some big movies that came out were, "Cabinet of Dr. Caligari","Dr. Jekyll and Mr. Hyde","Nosfertu", and "Dracula". Because the horror film is so closely tied to the monster it utilizes like in the Cabinet of Dr. Caligari it's Cesare who lies in the cabinet and murders at night , or the infamous Dracula.