Concerning me, I had a problem with the game. That's why I left for a long time. But your topic is the perfect opportunity to say I'm back !
A few years ago, I couldn't log in the game for no reasons. I pass the details, but I tried everything I could do to fix it, but nothing worked. I was desperate I couldn't play that game anymore, and I was more desperate because of some "children players" who had trash talking to me during my last connexion. So I gave up...
Of course, as cosmohause said, I also had my adult life with busy stuff, and others video games to play (not much playing as a wolf character though...). So I forgot FH for a while...I don't know...5 years ? 6 ? 7 ? Even if I didn't uninstall the game, I didn't play...until today !
I don't know how it's possible, but today, just after the new year, I remembered the game and tried to log in just in case, and it worked !!
It's Christmas again !
So to answer your question, there are many reasons that could make people leave the game (busy life, connexions problems, bad people in the game...), but it doesn't mean that some old player won't come back, or that new players would join, or that the game will die soon ^^
I wanted to answer your question, but I also wanted to share how much I'm happy to play this game again, sorry if that's bothering ^^" Hope to see you in game. Take care and happy new year again !