I suspect the mechanism driving this goes all the way down to basic biology. Everything is a spectrum. Take gene regulation networks or protein-protein interact

I suspect the mechanism driving this goes all the way down to basic biology. Everything is a spectrum. Take gene regulation networks or protein-protein interaction networks. They are both extremely complex and nonlinear. Perturbations to one gene can lead to positive or negative regulation of a cascade of other genes, as well as negative or positive feedback loops. For these networks, there are many such "steady" states where the combination of gene expression leads to a healthy cell/organism. Biological networks also have a high degree of redundancy with many proteins having overlapping function. There is no such thing as a universal healthy state because any single cell can be in a wide spectrum of states but still function "good enough". I think the ultimate goal of medicine is to understand how each change in state, at the cell or organ level, changes state at the organism level. With that knowledge we can "tune" health in the right direction.