Why have capacitors improved so much over the years?


Assuming they have, which is my general impression…
redwoodaudio
I don't know much, but I would guess it's a result of materials research and testing as well as more precise manufacturing and better lead wires.
Tech is nothing more than a physical description of the ways they are different. Why they got better is audiophiles obsessed with and driven to achieve exceptional sound quality. How  they got better was by trying out and evaluating different ideas by listening.