Thermodynamics and entropy, while causing decay in the long-term, have nothing to do with human decay over the span of 80-90 years.
Arguing that entropy is THE fundamental cause of death just shuts down the conversation.
A causation is the way to describe reality, not the fundamental feature of the reality. And so, the causation should follow the goals of researchers. While searching for ways to live forever, we will not benefit from evolutionary explanation (we cannot fix evolution to get longer lives), but thermodynamics explanation could be useful (if its true, of course). So, thermodynamics is a good candidate for the role of "fundamental cause".