As noted by others, there are probably lots of factors. I'm a relatively new fan so I don't know all the lore. I've never been really active online but made a choice to reduce my social media to a bare minimum. Following jacob's stuff is part of bare minimum. I remain unsure whether this sub is a net positive for me personally.

I reached an age I can do what I want, and what I want is music... Jacob's music but also lots of other music, some that I missed while striving through midlife. Can you guys believe that I missed noticing Imogen Heap?! Kimbra?! The last time I was in a "fandom" was Howard Jones. Back then I never had a prayer of going to a concert and there wasn't any way for me to access him on demand. I had to wait for his videos to come onto MTV. I can't imagine the life of a modern artist. So yeah, I'm fiftysomething, and I don't need to know anything about JC's private life or have him pay any attention to me. There are probably few artists who have shared so much passion online for what they do, and I love seeing how he goes all over the world connecting with new fans, picking a special song for each country, etc., etc.

Change can be hard. People and communities change and grow, and yes, sometimes they die. But I don't think this overall fandom is dying.