I am 100% biased but owning your own data, more control over UI and building up an archive of content is priceless when you compare it to a social media or an app based platform like Slack/Discord.
I would add: our forum is serving as a single source of truth for all things support, feature request, and bug report related. Everything is out there in the open, which I love for transparency sake.
Also, one random feature i love in Discourse specifically is the suggested answer feature while you are typing. This helps prevent the same questions getting asked every day. Brilliant.