Presumably people who break those laws think that the reward > (risk * penalty). They probably think that they won't get caught or if they do, hey, do your 5 years and get out. So either we need to increase the risk or the penalty.
In the mass shootings I have heard of I don't know any of them that had a real plan to escape death or capture. What is the incremental penalty that you are going to impose on top of suicide or 27 murder convictions that would have made a difference?