It’s not that we can’t fix things— given enough time and resources. It is just that we need to fix too many things. Each thing fixed only makes a small difference to average uptime, and that will be true for a long time, unfortunately.

We got some big early wins from low hanging fruit of infant mortality and poor sanitation. Everything else moves the needle a lot less, and it is a really long bug list. Our environment does ongoing damage of many different kinds and we wear out.

It's actually both - a thing of wonder wrought up by tens of millions of years of mindless evolution. And most scientists would already be happy to be able to "hack" this incredibly complex system to achieve a certain goal (e.g. cure cancer), not "refactor" the whole code, as you seem to be suggesting.