But what about folks who just want to run a forum?
They can run one... but unless it has hard to find content, odds are that there are not going to be masses flocking to them that most new admins hope for.
But they need to have reasonable expectations as to the limitations of a site based around posts.
For those users that just want to find a place to post, there are generally more popular sites already around. Reddit is one simple example. You have a singular app with a singular sign in and tons of subs to subscribe to/participate in. So what extra does a forum only based site bring to the table over what Reddit currently offers with their wider exposure and larger existing user base?
There are some exceptions... but usually those are sites that have been around for years and were popular already. But even those type of sites are having issues with keeping a steady stream of regular users visiting. I know of several that I participate in that the posting has dropped of drastically over the last few years and it's usually a core set of people posting regularly.
And yes, there are folks that run a site just because they enjoy playing with either a particular script or scripts in general to learn from (I am one of those). But the most of them are very realistic in that they run their site for their benefit and do not have high expectations of it growing.
Of course, it also depends on the niche. If the site is just a chat type site then a forum only solution makes sense. But we are back to the fact that there are already tons of other sites of that type around so what does another one bring to the table that differentiates it from all those others.
Now, if it a more technical niche, having those other features are usually needed.
This is just a snapshot from GA recent traffic to my primary site.
As you can see, the forum link is listed, but it is also where you have to go to to access the other parts of the site. You see no threads or posts listed.