Forums and Lemmy work quite differently. For starters, forums are more suited for long-term discussions. On some of the forums that I’m a part of, a topic can be active for several years (except of course the ones which discourage necro bumping, like the Arch Linux forums). Whereas Reddit, Lemmy and the like are more suited for news and discussions around the “now”. Once a post falls off the front page, it’s gone from everyone’s consciousness. Although on Lemmy you could have your default view set to “active” which will bump up old threads which are active, but neither the default Web-UI nor any of the clients (that I’m aware of) do a good job of highlighting the new comments/replies since you last visited the thread. There’s also no easy way to subscribe to a thread (yes I’m aware there’s a bot for it but it’s not allowed everywhere). Furthermore, most clients also mark a thread you’ve visited as “read” (which is typically a greyed-out/dull color) and many don’t even indicate that there are new comments, which further discourages you to revisit a thread.

The second is that there’s less or even no importance given to upvotes. In fact most forums typically disable or don’t even have votes on threads, which means every thread that’s posted gets equal importance and visibility. As a result, you don’t get karma farmers / low-effort / clickbait posts, at least not the ones made with the intention to seek karma. And it’s the same with comments - because they’re arranged in a linear manner (and typically don’t have votes), every comment gets equal visibility, and you don’t need to navigate thru complicated nested threads to pick up new comments. Again, as a result of this you tend to see fewer low-effort/meme/troll comments.

Finally, the most important differentiating factor is the moderation tools. Many mods and admins here have complained at how lacking the mod tools here are, especially when we had those CSAM spam attacks a couple of months ago - there was effectively no way to stop new accounts posting that crap without turning off registrations completely and temporarily defedarating from some instances. But on a forum, you have several measures such as having a cooldown period of x days before you can post, or gaining gradual posting privileges as you complete more actions such as say, competing the new user tutorial, gaining karma from posting to the newbie/introduction forum etc. Some forums may set it such that new users can post but a mod might need to approve the post; or they can post text but not images and links (which would discourage spammers and trolls) until they have sufficient karma or account age. I’ve also seen forums have a “trust” feature where a mod can mark an account as trusted to give that user more rights/access.

There’s many, many more such features which make moderating and managing a forum a breeze compared to Lemmy, and for a heavily-moderated community like Beehaw which also values quality over quantity, old-school forums make a much better choice.