This is a setting (max consecutive replies) that can easily be changed to something else than the default of 3 if we want to.
Personally, I believe we should change the setting. This is one of several restrictions designed to solve a problem which the OSM forum community never really had as far as I can remember, even before we moved to Discourse.
In contrast, too many topics being created for recurring content like WeeklyOSM alerts is something that was considered a problem in the past, and posting these updates in a dedicated thread is the solution we’ve previously arrived at.
Using a tag may be an alternative solution to the same problem, with some benefits and drawbacks compared to the single-thread solution. But I think that the choice between these solutions should be made based on what works best for the particular topic and sub-community; imo they should both be available and not prevented by the forum settings.