Why is science just a starting point and not an end point?

Because the answers beget more questions, and the subject is infinite.

...silly boy....;)

Properly derived science contains only provable conclusions that are bedrock.
All the rest is conjecture - interesting but not the basis for anything solid.

The problem is bad science.  This is in the ascendency.  One reads the most obviously idiotic nonsense every day, often obtained by extrapolation.  Extrapolation is always bad science.

The one I like best was around 15 years ago.  'All the snow and ice on the Himalayas will be gone in 30 years.  Palpable stupidity at the time; we're about halfway there and there's plenty left.  I said at the time that if the entire Chinese nation went up there with blowlamps working 24/7 it wouldn't happen.

Because the answers beget more questions, and the subject is infinite.

...silly boy....;)

I'll assume that's not a scientific answer, so I hope you'll forgive me if I ignore it.

To what end? If I am going to need to listen to the audio equipment to decide how it sounds, what possible value does the results obtained from test tones give me?

Test tones can show distortion and noise better than music. Test tones are well chosen to stress the device under test. How much value you get from it is up to you.