We do it for the same reason nature does. Building new things is far easier than maintaining and modifying old things forever. It's a tremendous waste for old p

We do it for the same reason nature does. Building new things is far easier than maintaining and modifying old things forever. It's a tremendous waste for old plants and animals and humans to die and throw away all their accumulated resources and experience, but nature tolerates it because maintaining and/or modifying bodies over time eventually just becomes too hard. I can see some objections of the form "that's not why nature does it, it's because genes need to evolve". Well, nature could have had our own genes changing and evolving in our bodies over time, if that made sense. It doesn't. The root of the problem is it's too difficult to repair and modify old things. Much easier to throw away and replace. The difference is that nature recycles everything. But that isn't always constant. There have definitely been times in evolutionary history when places have been full of natural waste of one type or another and it took a while for nature to figure out how to recycle it. One day maybe we can get there too.