I'm glad Colorado has had better luck with kids in foster care than California. Perhaps they keep the number of children in the system low enough that they can carefully screen potential foster parents and only choose the very best ones.
You have to weigh the risks. In order to lower the criteria for removal of children in CO so as to have prevented these 13 deaths, how many more children would have had to be put in the system? Since we can only know from hindsight which children actually will die, we certainly can't assume the number of kids in foster care would be increased by only 13.
So let's say Colorado doubled the number of children in foster care, just to be on the safe side. Unfortunately, the risk to children in foster care would more than double because Colorado would have to lower its standards, training, screening practices, increase the incentives to become foster parents, etc. All these things would make foster care more risky for children.
You can't just remove children from their homes wholesale "to be on the safe side." There are risks on both sides, and when you tip the balance, you increase the risks on the removal side.