Even more, evolution is often 'ineffective' and also can't make big leaps without complete disasters. It is quick only when you die young, as you already mentioned. It could happen that aging became unneeded at some epochs/species, but there was no easy way and/or strong reason to "turn it off" again.

Our bodies are not well-designed, they are full of legacy. The whole idea of moving via contracting meat is... strange. For real, lower half of me exists only to move the upper half. That's crazy.