Linux

I disagree that the implication is only about lack of awareness. Further my point wasn’t that Linux is underused because of a lack of awareness. My point is that user popularity is not a valid measurement for usability.

Awareness definitely plays a role in user numbers but there are other more important factors. For example awareness of Linux doesn’t beat what comes preinstalled, this is a much bigger factor if we are talking about all desktop users in my opinion. Linux could have the best usability out of all desktop OS, most would still not change preinstalled OS for different reasons e.g. not knowledgeable enough, indifference etc.. You might argue that if it was the OS it would come preinstalled, but then you would be ignoring the economic reasons that guide that. I still maintain that popularity of an OS is not a metric that can be used to infer usability. As long as there are different hurdles to getting to the actual using part, actual usability can‘t be determined by popularity.

On a side note about awareness:

Maybe it's a generational thing?

It could very well be, or it could potentially be something geographical. Anecdotally in my friends group of university students(20-26year olds) in a non-technical-field, not a single Person (beside me) knew what Linux was, and most had never heard the term before I mentioned it in a conversation. Neither would my parents. So maybe not a generational thing. I think you might be viewing the extent of awareness from the eyes of someone broadly in the tech field?