I'm certain that the hobby of watches will be around for a long time even though a lot of people aren't into it, most people I see out on the street are just wearing cheap fashion watches from brands like MVMT or Apple watches, I've seen a few people with some nice watches in public or G-Shocks and it's actually how I made a good friend around the same age as me who is also a collector, I am only 20 years old and I got my first Seiko(SKX009) two years ago on my 18th birthday from my family(hence my name)
That's really what got me into watches and collecting them so that gift is very important to me even though it's just an SKX, like Ikuo Tokunaga said "Please touch your own favorite watch with your kind heart and love for ever." But that also goes for the people who buy fashion watches, if somebody enjoys a fashion watch from MVMT or Michael Kors then that's the watch they love and there's nothing wrong with that.
But it's not just that, in the world we live in today the people I know at least, I can't speak for everybody but they just aren't into watches as a hobby, they just see them as something they wear to look nice each day, in short they aren't collectors they just enjoy watches for fashion.
However I myself got into vintage Seiko's this year, I always wanted a pepsi 7548 because Gen Schwarzkopf wore one and he is for sure legendary to me. I had no vintage Seiko's in my collection until I bought my 7548-700B and I found this forum a few days after I bought it from googling questions I had. So I can't really say 100% why the hobby isn't growing, but this is at least my perspective.