I use this sort of app, have for years. The idea of using a chatbot as UI is completely unappealing. So I think it comes down to there not being a need for this new take on this concept.
Yes totally, I thought "hey using a chatbot would be like texting an accountability friend or coach" but in reality that gimmick just doesn't work. Since tracking habits requires displaying data, a user interface with visual elements is more effective than a chat UI.