I'd say Discourse makes a different set of tradeoffs, and a large percentage of people are fine with those tradeoffs. Discourse could use some alternative clients for sure, and it'd be even better if there were a standard for such clients to coalesce around. It seems these days all the effort around standardizing such a thing is in the fediverse, which is a fine idea but ActivityPub is a an over-engineered monstrosity of a spec that results in incompatible clients anyway.