Earlier quoted context omitted.
We don't even know what all the factors are, and we don't have a practical or affordable way to gather and record all that data in a high-quality, consistent manner.
So we don't even start to try? That's not a good enough reason. Given the social and financial magnitude the excuse is nearly criminal.
We can do somewhat better at measuring quality for larger provider organizations across patient populations. The NCQA HEDIS measures are evidence based and reflect current consensus on best practices.