Why have capacitors improved so much over the years?

Lou, what a well articulated post! Some of your quotes are priceless!

Yes, Lou's post was very good & made for some interesting reading. I can't understand either why manufacturers go through all the trouble of designing a piece of gear & then at the most critical point insert cheap caps.

I can't understand either why manufacturers go through all the trouble of designing a piece of gear & then at the most critical point insert cheap caps.

For one thing, a large manufacturer might pay a dollar for a cap which you might pay ten.

Adding $100 in parts cost is $500 out the door and $1000 in the store.

Many of the improvements effected by the great unwashed may be seen as detrimental by the designer in terms of sonics, reliability, etc.

An engineer, be it an all out, no holds barred or LoFi PoS has a specification of what it to be achieved and a budget to hold. Better caps could result in a flimsy chassis, under-sized heat sinks, lower quality PCB, cheaper switches, etc. etc.

There are plenty of Best of Everything manufacturers and their prices reflect it.

How many Joe HiFi tweaks are verified in engineering terms? Joe may think it better, but most may not.

I can't understand either why manufacturers go through all the trouble of designing a piece of gear & then at the most critical point insert cheap caps.

When design engineers select components/parts for their circuitry, it is their responsibility to assure all components/parts are up to required specification and not to compromise safety and reliability.
Most boutique audiophile capacitor manufacturer cannot provide required documentation for design engineers to consider installing such capacitors in the design.

@widmerpool Absolutely correct.  Even table salt versus Kosher salt.  And even among brands of salt with Diamond Kosher salt generally superior to other brands.