Why have capacitors improved so much over the years?

While the referenced page is extensive, it's also a lot of hooey as components perform in concert with their containing circuit. There is no absolute and cost is seldom an arbiter of quality.

More than once, "Wow!" devolved

@millercarbon - that link has been posted in this thread already.  The original question was actually “why” though…

"Why" was answered in the third post.