Why on earth?

I guess the worst clips are those that try, well meaning but wrong, or intentionally false to sell their product, to be technical or objective. 

One well meaning attempt by a subjective reviewer to do an objective test of USB cables described a test where about the only thing not a variable was the cable. Well meaning, but a complete lack of understanding how A2D and DACs work. Even darn smart people, like a long presentation by a high end DAC designer had a couple serious mistakes. Suspicious as he used them to denigrate competing technology.  Even out "favorite" objective scientific reviewer only does the measurements his box lets him do and yet the chief engineer of that test box emphatically states it does not measure everything and the measures it does make do not describe how we perceive sound.  I guess those are more dangerous than some clown playing sound clips on two speakers. 

I use my and my wife's ears.  The You-Tube has identified brands I never heard of, so that's something. Direct sales seem to be totally dependent of social media. The only help the old, mostly gone, print media had was one annual summary of manufactures. OH, one Audio article by Walt Jung was a big help in understanding caps for a noise problem we had at work. I used his lesson to solve a spurious NMI to a Z80 based system. Jan Didden's publication is very good but not exactly mainstream. Classical measures are a small help. Kipple or APx5.. measurements etc. Once half decent, then it is about hearing. 

I think the idea of this is to give you an idea of how they do sound. What really to me is a waste of time is to have a reviewer talk endlessly about his impressions of what he heard without a demonstration. You should be able to get an idea of maybe how they do sound because you are familiar with how your speakers present the sound that you have been listening to on the youtube video. Otherwise they are just moving air and wasting time to me.

What you get is a crude combination of the characteristics of your playback system and room acoustics layered on top of a crude combination of the poster's system and room acoustics, plus the very crude characteristics of the microphones employed and recording techniques, etc.  It is ridiculous to then try to isolate the difference one piece of gear makes in this mess.  A friend of mine toured a recording studio and was shown a room full of microphones.  There are some artists who will request a very specific microphone--not a particular brand or model, but a particular microphone because the difference matters to the artist.  Do you think any of these posters have that kind of selection and special microphones to capture the essence of the gear being auditioned?

The testing folks are also a bit unrealistic.  They often post frequency response, waterfall plots, etc. of speakers and comment as though those tests give definitive results.  Wholly apart from whether the tests really measure what we perceive and like, the tests themselves don't accurately measure what they purport to measure.  Manufacturers looking for good measurements send their gear to a testing lab in Washington state that is built inside a nuclear reactor facility that was never commissioned.  The main testing room is behind many feet of concrete and the room is gigantic (something like 450 feet long and wide).  The testing facility certifies that it can accurately measure speaker frequency response down to 25 hz.  Now tell me how some backyard or garage setup can give accurate measurements.

Generations of yoots loved the sound quality of mp3, those golden ears are still out there, they hear differences we cannot possibly hear. They can probably hear the magic difference of various fuses in equipment online.