We are left to infer why Desdemona claimed that she was to blame for her murder and can only surmise that she understands her innocence left her open to the manipulations of those around her. She never put two and two together. She just rolled along and acted like the innocent she was. She didn't see the treachery that surrounded her, her innocence and love for her husband renedered her blind. Thus, in the end, she blamed herself.
Explanation: Hope this helps! :)