Anyone with an interest in audio is at liberty to spend as much money as they wish. Some may simply want maximum sound quality for their money, some may want certain features eg tone controls, equalizers, USB inputs, some may want certain aesthetics, and some might want it all.
What nobody wants is to waste money on products which have no substantiated qualities other than some sporadic accompanying spiel. This is commonly the case when it comes to cables, contact enhancers, conditioners, spikes etc
It wasn't that long ago when some enterprising individuals realised that they could make far more money simply by rebranding stock cable and taking out a few high profile ads.
Forget about years of R&D and advanced engineering, that's way too hard and way too risky an investment. This is the way to go for a fast buck. Many have followed since, and many more will follow.
Now we see all manner of such products all purporting to enhance listening pleasure, competing on the market.
The OP is basically asking why some people dare to question the claims behind these products. Perhaps he should be asking whether any of these products have actually made any difference in the history of audio other than to the bank balances of the concerned parties.
Of course it's always up to the individual to decide how they will spend their money (funny how so few tweaks are free) but it does leave a bad taste in the mouth of those who have been swindled in this manner.
So it's only fair to warn the inexperienced. I would say that if you want to try such a product then at at the least make sure that you have a decent no quibble money back guarantee. That way you can be at least a little more confident in the veracity of the vendors claims.
The old Latin phrase caveat emptor (buyer beware) is shamefully relevant in most things audio. I hope that answers the question.