One of the biggest issues (and this is not limited to the forum script itself but 3rd party developer) is ignoring suggestions and having a "not originated here" attitude.
I don't think any paid forum script will ever be able to compete with FaceBook/Twitter and the like as they don't have the deep pockets that those social media companies do to pay for studies and research specific to their offering.
A really weak spot with at least one script I know is their basic implementation of functions.
Companies/developers would go a LOT further if they would announce a basic function that they were already planning and then get outside feedback on how what they are offering might be improved over their initial plans. Heck, they don't even have to announce it to the general public. They could easily contact several of their active users on their support site and request feedback.
Once more, I'll refer to a solid script (not by name) that has a feature called custom fields (forum, media, 3rd party add-ons, etc can use them). You can capture all kinds of neat information using them. The function has been around for years. But NONE of it is discoverable via search, even if paying for an enhanced search add-on. It was something with this particular script that was suggested 6 years ago in 2018... and still has not been implemented (although it may be in 3.x, but I don't go over to that site any longer and don't keep up with the latest cult giddy giggle gossip).
Then you have another software provider (Invision) that is at least now somewhat accepting of input from their license holders and attempting to offer them items of import to the license holders and their users.
One of the major problems that impacts ALL scripts... there are only so many ways you can present the content when collected in a format that a typical forum does. The area that really needs to be worked on is the ability to ease the reading and collection of posts/content on mobile devices. Even PWA doesn't fully offer what dedicated apps for FB/Instagram/Twitter/Whatever can. But then again, those are single access sites and they can design their mobile app to fit their site.
My XenForo site would not work well with an app that worked well with this site. I offer functions/features that this site does not and vice-versa. So expecting a centralized app that would fit every website using the software is rather unrealistic.
Tapatalk is a good example. It gives a consistent posting process across multiple script providers offering. But it does so in a VERY limited manner. If I had it available on my site, of the 10 "offerings" you can avail yourself of via web/PWA (forum, gallery, reviews, articles, link directory, clubs and more), you can only access one of them, the forum.
Discourse was mentioned.... and in some ways it is progressive, for a general conversation flow. But they also only offer a very limited feature-set when compared to other scripts. Want a gallery/media component? Too bad. Want a centralized resource offering? Too bad.
But their presentation of the site discussions? Lipstick on the same old pig.
Want clubs? Too bad.
