I have seen a few recently that were linked to. The tutorials were not all that old, posted within 6 months or so, but the code they teach is well out of date. Things like mysql_, md5 and other such nastiness going on there.
Yes, there may be lots of good tutorials out there, but there are also many bad ones too, and newbies are often not educated enough to distinguish between the two.
I think forums are still popular among those who still use them, but I have noticed here, it is much quieter than it was a few years ago.
I think previously made topics can be a good reference for “lurkers”.
When I get stuck, usually my first port of call is reference a manual (Eg, php.net for PHP problems). Then if I’m still stuck I may do a search. Often I will find an answer here or on SO. I have never been active or had an account on SO, but I can’t tell you how many times I have found answers there. To me this shows that forums can be of use to people who don’t actually engage with the forums, so I imagine they get quite a lot of unknown, anonymous use, besides what you see.
And if I’m still stuck, I may ask here as a last resort, no offence… 
I think there are other reasons why people as individuals come and go from forums. Bearing in mind that this discussion may not just be about web-development forums, there are forums on a great many other topics.
In my previous job I did a lot of work on 3D/CGI and joined a forum for a particular software that I used, initially to get answers, but over time I realised that my years of experience with the software gave me a lot to offer the community and I started helping out there, becoming quite an active member. After a while I had made a bit of a name for myself there, and if I say so myself, became one of the “stand-out” members.
Then at some point, the company stopped paying the subscription for my software. That meant I was stuck with the same version for the years to come, while others moved on to newer ones.
To make a parallel to that with web development, it’s like being stuck in an age where you are developing for an IE7 era, or PHP4 or something, while everyone else is moving on to HTML5, CSS3 and the likes. I still had the broad knowledge of the fundamentals and pre-existing tool-set. But there was a whole load of new stuff to discuss that I never got to play with and felt a bit left behind. I think at that point my activity started to dwindle. The final nail being a (unplanned) change in occupation, where I no longer work in that field. A bit sad really to drift away from that community, as this was not necessarily by choice as such. But there is not reason I would not return if my career went back in that direction.
Now my work is primarily web-based, which means I spend more time hanging out in this forum. Though I think of late I have not been as active as previously. Not through lack of interest, but more a lack of spare time.
There is another usefulness of forums this experience has taught me. Giving away a secret here; being a “helper-bee” in forums is not entirely an altruistic thing. It is a very effective way to hone your own skills and confidence in whatever field you cover. I found both here and in the 3D forum, that the wealth of knowledge from other members rubs off on you and tacking other people’s problems really helps you develop your own problem solving skills and broadens your experience. While seeking out answers to questions you did not ask yourself, expands your knowledge in directions that you did not know it needed to. On top of all that, you are helping someone else out at the same time.
So in summary, I think forums are a great thing and would not like to see them fade away. I think they are particularly suited to the more deeply technical subjects, as opposed things suited to the throw-away chit-chat of social media which is forgotten about after a day or so.
