In a similar vein, too sports sites that I follow which used to have vigorous discussions during every game and about every aspect of the teams are also vastly smaller now yet you get prompts to "follow" every single baseball player on X, Rumble, and those other platforms even if they hit less than Mario Mendoza.
The Forums may have to change and even then may still get overtaken by the shift in communications preferences by different generations, as BackDoc pointed out.
Interestingly, while I'm of the generation that first saw Bigfoot on In Search of and The Six Million Dollar Man, I lost all interest in it until the early 2010s. And even then my first reaction was, "this really can't still be a thing, can it?" So I agree that as us older folks move on, the Forums will likely shrink because younger folks aren't as interested and don't consume news the same way.
Matt Moneymaker made a comment on a recent Bigfoot and Beyond podcast that younger researchers he has met haven't gone back any further than Finding Bigfoot. When he asks about John Green or Grover Krantz, he gets a blank stare and a "who is that?"