Of course it would be tautological to say "what's useful is useful" but that's not what the parent is saying.
The parent is saying that usefulness is the main, if not only, cause of success, and that other factors are in fact irrelevant (namely, fashionableness, launch strategy, celebrity endorsements, etc.)
You can agree or disagree with that thesis, but here you're misrepresenting it.
“Usefulness” is not a metric that can measured or sought in isolation. Usefulness needs an actor trying to perform an action desiring a result.
When OP says something failed because it isn’t useful, they are deliberately ignoring the subject and object of the equation.
When the article says that influencers didn’t glom on to Spectacles, they are making a statement about influencers not finding it useful but if you read the parent comment, this observation is useless because it obfuscates the true problem - that Spectacles is “useless”.
The parent is saying that usefulness is the main, if not only, cause of success, and that other factors are in fact irrelevant (namely, fashionableness, launch strategy, celebrity endorsements, etc.)
You can agree or disagree with that thesis, but here you're misrepresenting it.