Yeah I'm still around. I don't know what that makes me - a long-term enthusiast or a sad person with nowhere else to go!

In reality I do have somewhere else to go and I write - a whole lot more than here - on a couple of other websites. But over my years on forum-based websites I've seen a distinct change with identifiable reasons for it.
My feeling is that social media is drawing away many who might once have used forums. I am certain that's the case on one specific website where I'm a member and also a member of its Facebook Group's page. I see daily the huge amount of activity on its FB page compared with that on its near-moribund website.
The popularity of smart phones is the reason. They have instant online access along with platform simplicity - Facebook has done an astoundingly good job. A similar situation is seen with email, a medium more highly structured and slow to use compared with other instant-messaging apps. Email replaced letters and many formal documents; social media platforms are replacing email.
With websites I'm seeing that the more specialised they are the more limited is the range of subject categories and the fewer new members are likely to be attracted. It makes sense. Even sites with lots of forums can struggle to attract new members. Without new members, active members, sites get used by a comparatively small number of members. Some forums may become chat rooms, places the same few gather socially, rather than places for stimulating interchanges of ideas and views. In others may be found topics peddled by the same few voluble individuals with specialist agendas - anti-government, conspiracy theorists, UFOlogists, anti-vaxers etc. They contribute little to discussion quality but the quantity of their postings may positively influence search engine results. In turn the website is more easily found by seekers looking for other topics.
Websites with a highly specific focus such as the afterlife or Spiritualism attract few new contributors. Folk may come looking, some will register for an account, but few become contributors. Existing members naturally have less to say, the number of new postings drop so search engines may not show the website to searchers who might otherwise have become active members - I receive speculative approaches by search engine optimisation companies offering to raise the profile of this website
If my summation is wrong then there must be reasons I'm not aware of.