Insulin injections done wrong!

They didn't messed up diabetes as bad as other movies but there is one thing bothering me. Insuling injections are supposed to be given subcutaneous, meaning the injection should be given under the skin, into the fat layer. In the movie they are shown to be intravenous, meaning into the vein. Insulin given directly into the vein does not happen. Why is it so hard for movies to get diabetes right?