Why on earth?

I think it can be a valuable tool in some minor respects.  Ana(Dia)log does some A/B comparisons where you can hear the differences I demoed equipment.   Obviously everything is filtered though a less than ideal chain, but it does give you a valid idea of the differences in reproduction.

I don’t purchase based solely on this, but it help cut through so much noise on otherwise undemoable equipment…

Yes we are that stupid. Because there are people getting rich from posting crap on the various "social" media platforms mostly about mindless drivel and I'm guessing most of us here have missed that boat.

The upside is we are not contributing to the decline of the human race.

FYT.

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.