I think this is the reason. A quick browse reveals that most of these “communities” are basically paid advice channels or “courses” for influencer-type people. This is a really popular method for generating income especially in the influencer/guru space.
So the fact that it has no barrier to spin one up monetize it are the primary features. In this way, it’s driven from the top down - influencers bringing people to the platform. In contrast, Discourse definitely feels more like a platform meant for grassroots communities built from the ground up. Similarly, these individual Skool pages feel like something meant to last a few months to a year, whereas a Discourse site feels like something meant to grow over a decade or more.
I think the different intention behind both platforms make it hard to do a direct comparison. But if Discourse did want to take some of this influencer marketshare, the top three priorities I would point to are 1) make it effortless to spin up a community 2) more monetization features and 3) more themes that make it look less like an old fashion forum