Because once you build up a picture of where most of the blame lies for deaths and injuries to cyclists then it gives you the more important areas to tackle first in improving safety, If for arguments sake most of the fault was with the cyclists themselves then maybe it's time to start looking...
It's sad that so many cyclist's were killed, But to build a correct picture of where the blame lies you also need to know how many cyclist's died because of their own actions and how many were down to the actions of others.