Do you actually have any evidence to claim this "fact" is accurate? I know a lot of people who own PMPs and portable headphones/IEMs. All of them have times when they just sit on their couch and just listen to music. I've also seen plenty of people (young and old) sitting on a bus/train/public bench/etc with the earbuds and they are just listening to music - not doing anything else. Does one have to be sitting at home, in a special room, to be considered to be listening to music as a singular activity?
Despite what has already been said in this thread, you seem to be making up this "fact." Music players have become cheap and ubiquitous and so you see more people listening to music now. 30 years ago you were forced to sit at home and listen to music and only a select handful of people could afford the time and money to listen to music as a singular activity. If you were a working adult with kids, maybe you listened to an hour or two of music on Saturday morning, and you could only do that if you had the peace of mind to sit down focus only on music. Things are different now. More people can enjoy recorded music and you can do it in a wide range of situations.
I've talked to many people who just say that music is for "on the go." Some say they just listen to it to have the noise as a comfort or relief from complete silence. I do agree, some people just sit and listen, but music is generally regarded as an activity to waste time, not use it. I think if people got a pair of SR-60is or something along those lines, they could realize the potential of their music. I know when I used to use my old Skullcandy earbuds, at the time I didn't realize it, but it was like I was disconnected from the music. I didn't feel captivated or anything. It just seemed like noise. But when I came into this world of hi-fi (or headphone hi-fi) I felt I was truly enjoying the music. It captivated and impressed. Which is why when people have cheap/bad headphones or speakers, you won't find them listening to music as much. Just the noise
I also agree with the whole portability issue, as I said before, it means more music for the people. But again, it generally makes people think of music as an activity to provide noise on a bus, that's better than the whole crowd of people's noise. I know everyone I've talked to in school at least have admitted music as noise to occupy their time, not music, noise. They mostly listen to dubstep (which I have no problem with) but cranked up to volumes where you're actually missing parts of the song it's so loud. Also, most of them only have one earbud in so they can hear their friends. believe me, I've also heard numerous adults mention music as a background activity. It just seems like true enjoyment of the music is seeping away, leaving us with people who only want background noise, not really listening to the intricacies of music.